Add support for Python type parameter lists

[jbms]

Sphinx has partial support for type parameter lists: they are supported by the Python domain in signatures, but are not supported by autodoc.

This adds the following support:

• Sphinx Python domain for type parameter fields in docstrings, with sphinx.ext.napoleon support as well.

• Support for type parameters as Sphinx objects, with cross-linking, like the existing support for function parameters as Sphinx objects.

• Support in apigen for PEP 695 type parameters, and for displaying pre-PEP 695 separately-defined TypeVar types as PEP 695 type parameters.

[jbms]

This is basically feature complete but still needs some work on documentation and testing.

[jbms]

The build failure due to undefined reference T is odd --- the build succeeds on readthedocs and I also can't reproduce the issue locally. I will have to investigate more.

[codecov]

Codecov Report

Attention: Patch coverage is 62.72727% with 123 lines in your changes missing coverage. Please review.

Project coverage is 63.87%. Comparing base (7796775) to head (76ab811).

Files	Patch %	Lines
sphinx_immaterial/apidoc/python/apigen.py	32.50%	54 Missing ⚠️
...phinx_immaterial/apidoc/python/type_param_utils.py	74.26%	35 Missing ⚠️
...hinx_immaterial/apidoc/python/parameter_objects.py	72.11%	29 Missing ⚠️
...terial/apidoc/python/type_annotation_transforms.py	50.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #366      +/-   ##
==========================================
- Coverage   63.91%   63.87%   -0.05%     
==========================================
  Files          67       68       +1     
  Lines        8068     8359     +291     
==========================================
+ Hits         5157     5339     +182     
- Misses       2911     3020     +109     

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[jbms]

CI now passes.