Add compiled local partition lifecycle

[insujang]

Summary

• split process-group-independent ownership compilation from partition activation
• add explicit uneven pipeline stage specifications and stable logical state manifests
• preserve the reusable model blueprint across partition swaps
• add idempotent context retirement while keeping homogeneous materialize() compatibility

Why

Oobleck must choose rank-local ownership before WORLD exists and repeatedly replace heterogeneous pipeline partitions across membership generations. These generic lifecycle hooks keep elasticity policy in Oobleck while making Cornstarch partitions reusable.

Validation

• pytest -q tests/distributed/test_compiled_plan.py tests/distributed/test_compiled_plan_direct_import.py (5 passed)
• exercised by Oobleck real synthetic Llama one-step integration

This PR intentionally targets refactor and should remain open for upstream review.