test(evm-module): skip RandomSampling fairness + gas benchmark under coverage (fix coverage CI on main)

[branarakic]

What's broken

main's Tornado: Solidity coverage (push safety net) lane is red: npx hardhat coverage exits 1 with 1 failing test —

@unit RandomSampling > Phase 10 — value-weighted challenge generation
  > fairness: draw frequency within ±2pp of weight share (settled state):
    Error: Timeout of 600000ms exceeded.

All 781 tests pass locally under coverage (12m); on CI the run takes ~34m and the 5000-draw fairness test tips past the 600s mocha timeout under instrumentation.

Cause

Introduced by #1226 (the BIT sampling PR), which added two timing/gas-shaped tests without the coverage guard the repo already uses:

• the fairness statistical test (5000 previewChallengeForSeed draws), and
• the @gas benchmark suite.

Under solidity-coverage every draw runs heavily instrumented, so the fairness test blows the timeout. Neither adds unique contract-line coverage (they re-exercise the same paths).

Fix

Guard both to skip under coverage, matching the existing convention in ContextGraphStorage.test.ts:

const skip = process.argv.some((a) => a.includes('coverage'));
(skip ? it.skip : it)('fairness: …', …)        // RandomSampling.test.ts
(skip ? describe.skip : describe)('@gas …', …)  // RandomSampling-bit-gas.test.ts

Verified

• Normal hardhat test: both still run + pass (gas 2✓, fairness 1✓).
• hardhat coverage: both skip (gas suite → 2 pending, "Coverage skipped for: …"), so no timeout.

🤖 Generated with Claude Code

[otReviewAgent]

Review Agent completed this review and found no issues.