[GG clean] fix: profile MRV2 CUDA graph and sparse DCP memory

[voipmonitor]

Summary

Reapply the useful MRV2 CUDA graph and sparse DCP memory-profiling fixes from previous PR #131 after resetting dev/gilded-gnosis back before the Jul 20 merge/revert block.

This PR is stacked on the clean #130 replacement branch.

Original PR

• Previous merged PR: [GG] Fix MRV2 CUDA graph and sparse DCP memory profiling #131
• Original commit cherry-picked with provenance: 83579ac7bf

Changes

• Account for CUDA graph and sparse DCP transient memory in MRV2 profiling.
• Add the related environment/config plumbing.
• Add unit coverage for B12X fused all-reduce profiling, DCP workspace memory accounting, breakable CUDA graph behavior, and speculator graph memory behavior.

Merge Order

Merge only after #141, and only after explicit approval.

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[voipmonitor]

Superseded by #149, which carries this MRV2 profiling/graph-lifecycle work on a clean branch based directly on dev/gilded-gnosis. #149 also includes the corrected concurrency follow-up and the complete targeted validation.