How do you speed up slow CI pipelines?

Slow pipelines kill developer productivity. Key optimizations:

1. Caching: Cache dependencies (node_modules, pip packages, Go modules) between runs.
2. Parallelism: Split test suites and run jobs in parallel.
3. Test selection: Only run tests affected by the changed code.
4. Optimized Docker builds: Use layer caching and BuildKit.
5. Self-hosted runners: Eliminate queue time and use faster hardware.
6. Fail fast: Run linting and unit tests first; integration tests only if those pass.