ci: add backend unit tests to CI workflow

[shivv23]

Summary

The CI integration-tests.yml workflow only ran integration tests, leaving the 162 backend unit tests in tensormap-backend/tests/ completely untested in CI. This PR splits the single integration-test job into two parallel jobs:

• backend-unit-tests: Runs pytest tests/ against the backend unit test suite
• integration-tests: Runs pytest ../tests/integration/ against the full integration suite

Changes

• Renamed workflow from Integration Tests to Tests for accuracy
• Added a dedicated backend-unit-tests job that runs uv run pytest tests/ -v --tb=short
• Both jobs run in parallel on PRs to main with separate checkout/setup for clean environments

Validation

• All 162 backend unit tests pass locally (162 passed in 2.54s)
• No changes to application code — only CI workflow changes

Risk

• Zero application code changes
• CI-only change that adds test coverage
• Both jobs run independently and in parallel

Files Changed

• .github/workflows/integration-tests.yml — split into two parallel test jobs

[shivv23]

Polluted with 10+ unrelated commits. Clean version coming.

[shivv23]

Hey @ivantha, I apologize for the confusion with these PRs. The issue was that my local Git state had a polluted index with uncommitted changes from other branches — when I created the branches from what I thought was a clean origin/main, those branches ended up containing 10+ unrelated commits from the stale branch history. Both PRs showed the same 10 commits (augment, export, interpret, compare, tune) because those commits exist in main's merge history.

I've since identified this and reset everything to a clean origin/main. I'm going to create fresh PRs with orphan branches — each containing exactly 1 commit with only its relevant files. They will have no shared commits and zero conflicts. Apologies for the noise!