GH-50957: [Python] Reject unexpected concat_tables keywords

[Sakshamm-Goyal]

Rationale for this change

concat_tables() keeps **kwargs only for the deprecated promote argument, but previously discarded every other key. As a result, keyword typos and apparently meaningful inputs such as unify_schemas were silently accepted without affecting the result.

What changes are included in this PR?

• Reject unsupported keyword arguments with TypeError before processing the deprecated compatibility argument.
• Document that promote is the only accepted extra argument.
• Add a focused regression for the reported unknown-key behavior.

Are these changes tested?

• Built and installed the current Arrow C++ minimal Python preset and an editable PyArrow from this branch.
• python -m pytest -q python/pyarrow/tests/test_table.py -k 'concat_tables': 9 passed.
• python -m pytest -q python/pyarrow/tests/test_table.py: 181 passed, 33 skipped.
• Changed-file Python pre-commit hooks: format, flake8, and Cython lint passed.
• git diff --check passed.

Are there any user-facing changes?

Yes. Unknown concat_tables() keyword arguments now raise TypeError, matching normal Python call behavior. The deprecated promote=True and promote=False compatibility path remains unchanged.

AI assistance

I used an AI coding assistant to help investigate the root cause, draft the focused two-file patch, and run validation. I reviewed and understand every change and can own and debug it during review.

Closes #50957

• GitHub Issue: [Python] concat_tables silently ignores unrecognised keyword arguments, including unify_schemas #50957

[uros-b]

LGTM!