Add local pre-commit hook for Codecov config validation

[blakedehaas]

Context

The repository previously used an external codecov-validator pre-commit hook that is no longer available. This removed validation coverage for codecov.yml.

Driving Requirements

Add a local pre-commit hook to validate codecov.yml using Codecov’s validation endpoint.

Implementation Requirements

• Add a local pre-commit hook in .pre-commit-config.yaml

• Hook runs something like:
  Shellcurl --fail --data-binary @codecov.yml https://codecov.io/validateShow more lines

• Hook should fail the commit if validation fails

• Hook should only run when codecov.yml is modified

Considerations

• Avoid reliance on unmaintained external repositories (which caused this issue)
• Ensure the hook works in dev container environments
• Keep implementation minimal and consistent with existing local hooks