Add support for PEP 750 template strings

[1borgy]

For reviewers

• I did not use AI
• I used AI and thoroughly reviewed every code/docs change

Description of the change

Add expressions for ast.TemplateStr and ast.Interpolation, which were added in Python 3.14. Round-tripping (e.g. tests/test_expressions.py::test_expressions) does not work with the conversion or format_spec fields, though this is consistent with the current implementation of ExprJoinedStr and ExprFormatted.

Relevant resources

• https://peps.python.org/pep-0750/
• https://docs.python.org/3/library/ast.html#ast.TemplateStr
• https://docs.python.org/3/library/ast.html#ast.Interpolation

[1borgy]

Looks like most of CI is passing, bar config/test_api.py::test_api_matches_inventory for python<3.14. The suggestion of make run mkdocs build did not generate any changes to site/objects.inv for me. For the sake of not overusing GHA runner resources, I'll wait for a maintainer's blessing before investigating further.

[1borgy]

combine all 3 version checks in this file into one block

[1borgy]

could also try something like

Suggested change

	*(["t'a {round(key, 2)} {z}'"] if sys.version_info >= (3, 14) else []),
	pytest.param("t'a {round(key, 2)} {z}'", marks=pytest.mark.skipif(sys.version_info < (3, 14))),