Update python versions (drop 3.9, add 3.14)

[kingbuzzman]

Drop Python 3.9 support and raise minimum version to 3.10. Add official Python 3.14 support with CI testing.

[Copilot]

Pull request overview

This PR updates the supported Python versions by dropping Python 3.9 support (raising the minimum to 3.10) and adding official support for Python 3.14. The changes modernize type annotations to use Python 3.10+ syntax throughout the codebase.

• Drops Python 3.9 and sets minimum version to 3.10
• Adds Python 3.14 support with CI testing
• Modernizes type annotations to use Python 3.10+ union syntax (PEP 604)

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tox.ini	Updated test environments to include py314 and remove py39
pyproject.toml	Updated requires-python to >=3.10 and classifiers to reflect Python 3.10-3.14 support
.github/workflows/main.yml	Added Python 3.14 test jobs, removed Python 3.9 jobs, updated PyPy version to 3.10
pytest_django/fixtures.py	Modernized type annotations: moved Callable import to collections.abc, replaced Optional[Union[...]] with pipe operator syntax
pytest_django/asserts.py	Consolidated TYPE_CHECKING imports and moved Callable import to collections.abc
docs/changelog.rst	Added entry for Python 3.14 support in v4.12.0
README.rst	Updated minimum Python version from 3.9 to 3.10 in documentation

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