Prototype batched Pachner proposals with deterministic commit

[acgetchell]

Goal

Prototype batched Pachner proposal generation for downstream sampling workloads while keeping topology mutation deterministic and failure-atomic.

Scope

• Generate candidate Pachner proposals in parallel from immutable topology state.
• Filter or group candidates by non-overlapping conflict regions.
• Commit accepted proposals in deterministic order through the existing Pachner proposal API.
• Report stale, conflicted, rejected, and committed proposal counts.
• Preserve validation and rollback guarantees after every committed batch.

Acceptance criteria

• Prototype exposes enough instrumentation for downstream Metropolis-Hastings experiments.
• Tests cover conflicting local moves, stale proposals, wrong-owner proposals, rollback on failed commit, and deterministic fixed-seed behavior.
• Benchmarks compare serial Pachner proposals against batched proposal generation.
• The prototype does not require true concurrent mutation of shared topology storage.