fix(dcp): support disposable A2A profiling channels

[FujitsuPolycom]

Summary

Add checkpoint/rollback lifecycle support for disposable PCIeDCPA2A profiling channels.

Temporary CUDA-graph profiling channels can now be discarded without leaking IPC allocations, closing channels that existed before profiling, or retaining temporary stream aliases.

Scope

• checkpoint the pool's existing channel boundary
• roll back only channels created after that checkpoint
• validate that a checkpoint belongs to the same pool
• reject checkpoint/rollback during active CUDA graph capture
• preserve pre-existing channel and stream mappings

This is independent of the selected-record transport PRs.

Validation

Focused tests cover successful rollback, preservation of existing channels, foreign checkpoint rejection, capture guards, stream aliases, and idempotent lifecycle behavior.

Design reference

This lifecycle fix supports the broader profiling and graph-validation work documented in GLM-5.2 Sparse CKV under Decode Context Parallelism.

Implementation, tests, and documentation were developed with OpenAI Codex assistance and manually reviewed.

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