Add usage cost smoke test

[vkryukov]

Description

Added a usage cost smoke test script to quickly verify usage cost fields across popular models. We no longer observe missing cost information after metadata for a couple of missing Grok models was updated, so this PR focuses on the smoke test script for ongoing verification.

Type of Change

• Bug fix (non-breaking change fixing an issue)
• New feature (non-breaking change adding functionality)
• Breaking change (fix or feature causing existing functionality to change)
• Documentation update

Breaking Changes

Testing

• Tests pass (mix test)
• Quality checks pass (mix quality)

Checklist

• My code follows the project's style guidelines
• I have updated the documentation accordingly
• I have added tests that prove my fix/feature works
• All new and existing tests pass
• My commits follow conventional commit format
• I have NOT edited CHANGELOG.md (it is auto-generated by git_ops)

Related Issues

Closes #81