fix: Pin Python to <3.14 to resolve docs build failure (#390)

#### Relevant issue or PR

The docs build CI was failing because `setup-python` with
`python-version-file: "pyproject.toml"` selects the latest available
Python version (3.14), which is incompatible with PyO3 v0.24.0 used by
pydantic-core.

#### Description of changes

Bound python to <3.14 until we finalize #388 and add official 3.14
support.

#### Testing done
CI

Author: xalelax