[refactor] typification of SearXNG (initial) / result items (part 1)

Typification of SearXNG
=======================

This patch introduces the typing of the results.  The why and how is described
in the documentation, please generate the documentation ..

    $ make docs.clean docs.live

and read the following articles in the "Developer documentation":

- result types --> http://0.0.0.0:8000/dev/result_types/index.html

The result types are available from the `searx.result_types` module.  The
following have been implemented so far:

- base result type: `searx.result_type.Result`
  --> http://0.0.0.0:8000/dev/result_types/base_result.html

- answer results
  --> http://0.0.0.0:8000/dev/result_types/answer.html

including the type for translations (inspired by #3925).  For all other
types (which still need to be set up in subsequent PRs), template documentation
has been created for the transition period.

Doc of the fields used in Templates
===================================

The template documentation is the basis for the typing and is the first complete
documentation of the results (needed for engine development).  It is the
"working paper" (the plan) with which further typifications can be implemented
in subsequent PRs.

- https://github.com/searxng/searxng/issues/357

Answer Templates
================

With the new (sub) types for `Answer`, the templates for the answers have also
been revised, `Translation` are now displayed with collapsible entries (inspired
by #3925).

    !en-de dog

Plugins & Answerer
==================

The implementation for `Plugin` and `Answer` has been revised, see
documentation:

- Plugin: http://0.0.0.0:8000/dev/plugins/index.html
- Answerer: http://0.0.0.0:8000/dev/answerers/index.html

With `AnswerStorage` and `AnswerStorage` to manage those items (in follow up
PRs, `ArticleStorage`, `InfoStorage` and .. will be implemented)

Autocomplete
============

The autocompletion had a bug where the results from `Answer` had not been shown
in the past.  To test activate autocompletion and try search terms for which we
have answerers

- statistics: type `min 1 2 3` .. in the completion list you should find an
  entry like `[de] min(1, 2, 3) = 1`

- random: type `random uuid` .. in the completion list, the first item is a
  random UUID

Extended Types
==============

SearXNG extends e.g. the request and response types of flask and httpx, a module
has been set up for type extensions:

- Extended Types
  --> http://0.0.0.0:8000/dev/extended_types.html

Unit-Tests
==========

The unit tests have been completely revised.  In the previous implementation,
the runtime (the global variables such as `searx.settings`) was not initialized
before each test, so the runtime environment with which a test ran was always
determined by the tests that ran before it.  This was also the reason why we
sometimes had to observe non-deterministic errors in the tests in the past:

- https://github.com/searxng/searxng/issues/2988 is one example for the Runtime
  issues, with non-deterministic behavior ..

- https://github.com/searxng/searxng/pull/3650
- https://github.com/searxng/searxng/pull/3654
- https://github.com/searxng/searxng/pull/3642#issuecomment-2226884469
- https://github.com/searxng/searxng/pull/3746#issuecomment-2300965005

Why msgspec.Struct
==================

We have already discussed typing based on e.g. `TypeDict` or `dataclass` in the past:

- https://github.com/searxng/searxng/pull/1562/files
- https://gist.github.com/dalf/972eb05e7a9bee161487132a7de244d2
- https://github.com/searxng/searxng/pull/1412/files
- https://github.com/searxng/searxng/pull/1356

In my opinion, TypeDict is unsuitable because the objects are still dictionaries
and not instances of classes / the `dataclass` are classes but ...

The `msgspec.Struct` combine the advantages of typing, runtime behaviour and
also offer the option of (fast) serializing (incl. type check) the objects.

Currently not possible but conceivable with `msgspec`: Outsourcing the engines
into separate processes, what possibilities this opens up in the future is left
to the imagination!

Internally, we have already defined that it is desirable to decouple the
development of the engines from the development of the SearXNG core / The
serialization of the `Result` objects is a prerequisite for this.

HINT: The threads listed above were the template for this PR, even though the
implementation here is based on msgspec.  They should also be an inspiration for
the following PRs of typification, as the models and implementations can provide
a good direction.

Why just one commit?
====================

I tried to create several (thematically separated) commits, but gave up at some
point ... there are too many things to tackle at once / The comprehensibility of
the commits would not be improved by a thematic separation. On the contrary, we
would have to make multiple changes at the same places and the goal of a change
would be vaguely recognizable in the fog of the commits.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/plugins/unit_converter.py

@@ -18,11 +18,14 @@ Enable in ``settings.yml``:
 
 """
 
+from __future__ import annotations
 import re
 import babel.numbers
+
 from flask_babel import gettext, get_locale
 
 from searx import data
+from searx.result_types import Answer
 
 
 name = "Unit converter plugin"
@@ -171,16 +174,16 @@ def symbol_to_si():
     return SYMBOL_TO_SI
 
 
-def _parse_text_and_convert(search, from_query, to_query):
+def _parse_text_and_convert(from_query, to_query) -> str | None:
 
     # pylint: disable=too-many-branches, too-many-locals
 
     if not (from_query and to_query):
-        return
+        return None
 
     measured = re.match(RE_MEASURE, from_query, re.VERBOSE)
     if not (measured and measured.group('number'), measured.group('unit')):
-        return
+        return None
 
     # Symbols are not unique, if there are several hits for the from-unit, then
     # the correct one must be determined by comparing it with the to-unit
@@ -198,7 +201,7 @@ def _parse_text_and_convert(search, from_query, to_query):
             target_list.append((si_name, from_si, orig_symbol))
 
     if not (source_list and target_list):
-        return
+        return None
 
     source_to_si = target_from_si = target_symbol = None
 
@@ -212,7 +215,7 @@ def _parse_text_and_convert(search, from_query, to_query):
                 target_symbol = target[2]
 
     if not (source_to_si and target_from_si):
-        return
+        return None
 
     _locale = get_locale() or 'en_US'
 
@@ -239,25 +242,28 @@ def _parse_text_and_convert(search, from_query, to_query):
     else:
         result = babel.numbers.format_decimal(value, locale=_locale, format='#,##0.##########;-#')
 
-    search.result_container.answers['conversion'] = {'answer': f'{result} {target_symbol}'}
+    return f'{result} {target_symbol}'
 
 
-def post_search(_request, search):
+def post_search(_request, search) -> list[Answer]:
+    results = []
+
     # only convert between units on the first page
     if search.search_query.pageno > 1:
-        return True
+        return results
 
     query = search.search_query.query
     query_parts = query.split(" ")
 
     if len(query_parts) < 3:
-        return True
+        return results
 
     for query_part in query_parts:
         for keyword in CONVERT_KEYWORDS:
             if query_part == keyword:
                 from_query, to_query = query.split(keyword, 1)
-                _parse_text_and_convert(search, from_query.strip(), to_query.strip())
-                return True
+                target_val = _parse_text_and_convert(from_query.strip(), to_query.strip())
+                if target_val:
+                    Answer(results=results, answer=target_val)
 
-    return True
+    return results