perf(query-planner): replace DFS transitive reduction with petgraph algo

[tninesling]

Replace the O(V*E) DFS-from-every-node reduce() with petgraph's dag_transitive_reduction_closure (Habib-Morvan-Rampon algorithm).

The StableDiGraph-to-AdjList conversion is extracted into to_toposorted_adjacency_list, which maps sparse stable node indices to dense toposort-ordered indices for the reduction algorithm. Redundant edges are identified by querying the reduction graph directly rather than materializing an intermediate adjacency matrix.

All existing call sites, operation order, and defer-edge recording behavior are preserved — this is a pure algorithm swap.

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