Speed up lint and test CI pipeline

[bpasquini]

Problem

The CI pipeline runs lint and tests on every PR. As the codebase grows, this will slow down the feedback loop for developers.

Goals

• Profile the current CI run to identify bottlenecks
• Reduce lint/test execution time
• Consider caching dependencies (pip, npm) between runs
• Parallelize lint and test jobs where possible
• Add timing output so we can track improvements

Suggestions

• Cache pip packages with actions/cache
• Run flake8/black and pytest in parallel jobs instead of sequentially
• Only lint/test changed files on PRs (optional, more advanced)
• Use a faster test runner if applicable

Acceptance Criteria

• CI pipeline completes in under 30 seconds for a typical PR
• Dependency caching is enabled
• Lint and test steps are optimized