ci: add 'quality' gate job and gate 'build' with needs; enforce ruff/mypy/coverage use before Docker steps

[anibalrojosan]

What changed in this branch:

1. Split CI into two jobs in .github/workflows/main.yml:

• quality: installs deps + QA tooling, runs ruff check ., mypy src, and coverage run -m pytest with --fail-under=80.
• build-and-push: now depends on quality via needs: quality; proceeds to train, verify model artifact, build/push images, run compose, and probe endpoints.

2. ruff, mypy and coverage were used for quality testing. Errors founded on scr/ and tests/ folders were fixed.

Why:

• Fail fast on lint/type/test errors to avoid building/pushing broken images.
• Keep runtime images clean (QA tools not installed inside images).
• Provide a consistent, reproducible quality bar for all commits/PRs.

Validation:

• CI “quality” job passed, and subsequent “build-and-push” completed successfully.

[harrueds]

Nice work master, I always learn something watching your job.