ProcPipeline and the run() helper are pure logic without test coverage.
Add unit tests for the identity filter, chained filter execution order, the
append() layouts, and the chain handling of run().
Signed-off-by: Jan Lindemann <jan@janware.com>
Assisted-by: unsloth/Qwen3.8-27B-GGUF:Q4_K_M with pi.dev v0.85.1