[BLD] Enable mypy lint in CI

[adit24dhaya]

Summary

• Add a dedicated Run mypy CI step so mypy failures fail the job (separate from pre-commit steps that use continue-on-error: true).
• Scope the mypy pre-commit hook to chromadb/ to avoid unrelated types shadow errors in sample apps.
• Add incremental [[tool.mypy.overrides]] in pyproject.toml for modules with existing type debt.

Fixes #2054

Test plan

• pre-commit run --all-files mypy
• pre-commit run --all-files check-yaml

[github-actions]

Reviewer Checklist

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Testing, Bugs, Errors, Logs, Documentation

• Can you think of any use case in which the code does not behave as intended? Have they been tested?
• Can you think of any inputs or external events that could break the code? Is user input validated and safe? Have they been tested?
• If appropriate, are there adequate property based tests?
• If appropriate, are there adequate unit tests?
• Should any logging, debugging, tracing information be added or removed?
• Are error messages user-friendly?
• Have all documentation changes needed been made?
• Have all non-obvious changes been commented?

System Compatibility

• Are there any potential impacts on other parts of the system or backward compatibility?
• Does this change intersect with any items on our roadmap, and if so, is there a plan for fitting them together?

Quality

• Is this code of a unexpectedly high quality (Readability, Modularity, Intuitiveness)