Fix ignored path handling in hashing configuration

[hotcodemacha]

Summary

Corrected Config.hash so ignored paths are joined with the model directory and validated not to escape it, ensuring ignore rules no longer depend on the current working directory

Preserved user-supplied relative paths in set_ignored_paths and added validation in add_ignored_paths for new entries, keeping all ignored paths relative to the model directory

Added a regression test to confirm that ignored files are skipped even when hashing from a different working directory

Checklist

• All commits are signed-off, using DCO
• All new code has docstrings and type annotations
• All new code is covered by tests. Aim for at least 90% coverage. CI is configured to highlight lines not covered by tests.
• Public facing changes are paired with documentation changes
• Release note has been added to CHANGELOG.md if needed

[mihaimaruseac]

Thank you!