[mod] addition of various type hints / tbc

- pyright configuration [1]_
- stub files: types-lxml [2]_
- addition of various type hints
- enable use of new type system features on older Python versions [3]_
- ``.tool-versions`` - set python to lowest version we support (3.10.18) [4]_:
  Older versions typically lack some typing features found in newer Python
  versions.  Therefore, for local type checking (before commit), it is necessary
  to use the older Python interpreter.

.. [1] https://docs.basedpyright.com/v1.20.0/configuration/config-files/
.. [2] https://pypi.org/project/types-lxml/
.. [3] https://typing-extensions.readthedocs.io/en/latest/#
.. [4] https://mise.jdx.dev/configuration.html#tool-versions

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

docs/conf.py

@@ -151,6 +151,7 @@ intersphinx_mapping = {
     "sphinx" : ("https://www.sphinx-doc.org/en/master/", None),
     "valkey": ('https://valkey-py.readthedocs.io/en/stable/', None),
     "pygments": ("https://pygments.org/", None),
+    "lxml": ('https://lxml.de/apidoc', None),
 }
 
 issues_github_path = "searxng/searxng"