Tune crossing-via estimation, clamp probability, and add tests

[0hmX]

Motivation

• Improve the heuristic that estimates via usage and make the resulting failure probability better behaved and bounded between 0 and 1.
• Add unit tests to lock in expected behavior for target nodes, single-layer nodes, coefficient usage, and clamping for large inputs.

Description

• Adjusted the coefficients used to estimate vias in calculateNodeProbabilityOfFailure to 0.65, 0.3, and 0.32 for numSameLayerCrossings, numEntryExitLayerChanges, and numTransitionCrossings respectively.
• Changed the used-capacity formula to const estUsedCapacity = (estNumVias / 1.8) ** 1.15 to reflect the retuned scaling and exponent.
• Add explicit bounding of the returned probability with Math.max(0, Math.min(1, approxProb)) so results are always in [0,1].
• Added unit tests in tests/solvers/calculateCrossingProbabilityOfFailure.test.ts that validate target behavior, single-layer behavior, coefficient math, and clamping of very large values.

Testing

• Ran the new test suite with bun:test including calculateCrossingProbabilityOfFailure.test.ts, and all tests passed.
• Tests cover calculateNodeProbabilityOfFailure returning 0 for target nodes, 1 for single-layer nodes with crossings, correct coefficient usage and formula, and clamping large estimates to 1.

---

Codex Task