Improve heap performance, add integer-only ops and exponent support, and safer reachability pruning

[beackers]

Motivation

• Speed up the search ordering to reduce overhead when exploring many states by replacing repeated full sorts with a proper binary min-heap.
• Improve accuracy by restricting arithmetic to integer results, adding exponentiation, and deduplicating per-pair results to avoid redundant branches.
• Make reachability pruning safer and prepare the code for bound-aware pruning by exposing bound metadata and tightening the canReach test.

Description

• Replace table.sort based priority queue with a binary heap implementation in min.lua using siftUp/siftDown and a priority(state) helper. (min.lua)
• Add M.setBounds, isInteger, and safePow helpers to states.lua, and wire bounds from knockout.lua via states.setBounds(TARGET_MIN, TARGET_MAX). (states.lua, knockout.lua)
• Extend ops to include a^b and b^a using safePow, and make division return only exact integer quotients (a % b == 0 / b % a == 0). (states.lua)
• Ensure M.calc emits only integer results and deduplicates results per operand pair to avoid creating duplicate next states. (states.lua)
• Simplify and harden M.canReach so it returns true when bounds are missing, rejects invalid bounds, and uses a conservative interval (-sumAbs, sumAbs) to check potential reachability. (states.lua)

Testing

• Attempted to run lua knockout.lua 1 36 5 6 11 to validate behavior, but the run failed because lua is not available in the execution environment; no automated runtime tests could be completed.

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Codex Task