test(R-W-03): fee-shape invariant regression for CommissionManager se…

[sh3ifu]

R-W-03 / UT-FIX-06 — fee-shape invariant regression tests

Unit-test group for the stablePercent <= multiplier^2 invariant added to
CommissionManager.setGlobalDefaults and setCommissionRule (fix PR for R-W-03).

Coverage

• Reverts InvalidFeeShape on the audit's brick config (9000, 1) and at
  the just-above boundary (101, 10), for both setters.
• Accepts the exact boundary stablePercent == multiplier^2 (100% fee,
  netAmount = 0, no underflow).
• Accepts (9000, 100) with the default multiplier — regression for the
  uint256 widening in the fix. The audit's literal multiplier * multiplier
  would overflow uint8 at 100 * 100 and wrongly reject this valid 90% config.
• End state: an accepted boundary config produces fee == amount /
  net == 0 in calculateFundsInCommission without underflowing.