feat(dbt): fast pre-compile validation for dbt projects in dirty mode (#122)

[tjirab]

🚀 What changed?

• Added --dirty (-d) command line option to the lint command.
• Implemented load_dbt_models_fallback in manifest.py to parse DBT project directory models and seeds on the fly if manifest.json is missing.
• Added git untracked/dirty files detection in dirty mode using git status --porcelain -u.
• Integrated overlay of dirty .sql, .yml, and .csv files over the compiled manifest.
• Achieved 100% diff coverage with comprehensive mocks in unit tests.

🤔 Why is this change needed?

To enable fast pre-compile linting/validation of dbt models that are dirty or newly added, bypassing the slow dbt compile step when not needed.

🔗 Related Issues (Optional)

Closes #122

✅ Next Steps / Checklist (Optional)

• All unit tests pass.
• 100% diff coverage achieved.