perf(exec): parallelize transitivity on ComputePool (#586)

[DecisionNerd]

Implements #586: parallel transitivity on ComputePool.

Closes #586

  

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Note

Parallelize transitivity triangle counting on ComputePool

• Adds parallel triangle counting in algorithm_analyze_transitivity.rs via a new count_triangles_parallel function that splits source vertices into chunks and runs them on the instance-owned ComputePool using rayon.
• Parallel execution is selected when compute_threads > 1, node count ≥ 3, wedge count ≥ 32,768 (TRANSITIVITY_PARALLEL_CROSSOVER_WEDGES), and a parallel compute pool is present; otherwise falls back to serial.
• Worker panics are caught via catch_unwind and converted to a structured AlgorithmError rather than unwinding across the thread boundary.
• Updates execution-resource-policy.md to document transitivity as a parallelized algorithm with the crossover threshold and chunking behavior.
• Behavioral Change: graphs with ≥ 32,768 wedges will now execute triangle counting in parallel by default when a parallel compute pool is configured.

^{Macroscope summarized a4b8685.}

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Reviewing files that changed from the base of the PR and between 39d3131 and a4b8685.

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• crates/graphforge-exec/src/algorithm_analyze_transitivity.rs

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[blacksmith-sh]

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//crates/graphforge-storage:graphforge_storage_test (Exit 101)	View Logs

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