Phase 2: Optimize job parallelization

[RAprogramm]

Task

Optimize CI workflow execution by parallelizing independent jobs and establishing proper dependency chains.

Implementation

1. Separate fmt, clippy, deny, audit into parallel jobs
2. Tests depend on successful fmt/clippy
3. Coverage runs after tests complete
4. Optimize caching strategy per job

Benefits

• Faster CI feedback (~2-3 min vs ~5 min)
• Better resource utilization
• Clear dependency visualization

Acceptance Criteria

• fmt, clippy, deny run in parallel
• Tests only run after quality checks pass
• Coverage job depends on tests
• CI completes in <3 minutes

Parent: #175