prevent assert usage in non-test code — add codemod, CI check, and contributing guidance

[Satyasubhash01]

No production assert statements were found in the repository, so no runtime replacements were necessary. This PR adds tooling and documentation to prevent future use of assert in non-test code and provides a codemod for simple automated fixes.

Changes
Add: [check_no_asserts.py] — CI/check script to fail if assert appears in non-test files
Add: [replace_asserts.py] — codemod (dry-run / apply) for common assert patterns
Add: [check-no-asserts.yml] — CI job to run the assert check
Update: [CONTRIBUTING.md] — guidance: avoid assert for runtime checks; raise explicit exceptions instead

Notes: codemod dry-run found no matches; no source files were modified.

How to test locally
Run the assert check: python scripts/check_no_asserts.py
Dry-run the codemod: python tools/replace_asserts.py
(Optional) Apply codemod: python tools/replace_asserts.py --apply
Run tests and linters: python -m pytest
flake8 || true
Rationale
assert statements are removed with Python optimization flags (-O/-OO) and must not be used for runtime validation. Explicit checks that raise informative exceptions are required for library/production code.

Signed-off-by: Satyasubhash01