test: add regression coverage for FxQuorumEvaluator validation

[priscannanna85-lgtm]

Overview

This PR adds focused regression coverage for the METRIC_QUORUM_EVALUATED failure handling in FxQuorumEvaluator. The evaluator throws explicit errors when k, tolerance, or reference are invalid; these branches previously had no dedicated tests, so silent behavior changes could slip through. This change exercises those branches, asserts the exact error contract, and adds neighboring success and boundary cases.

Related Issue

Changes

🧪 Quorum Evaluator Regression Tests

• [MODIFY] src/services/fxQuorumEvaluator.ts

  • No behavioral change to the public contract; validation branches for k, tolerance, and reference are exercised as-is.
  • Ensures the three throw new Error(...) sites remain observable and deterministic for callers.

• [ADD] src/services/fxQuorumEvaluator.test.ts

  • Failure paths:
    • k non-integer / k < 1 → FxQuorumEvaluator: k must be an integer >= 1.
    • tolerance non-finite / negative → FxQuorumEvaluator: tolerance must be a finite number >= 0.
    • reference not 'median' or 'mean' → FxQuorumEvaluator: reference must be 'median' or 'mean'.
  • Boundary inputs:
    • k = 1 (minimum valid) and tolerance = 0 (minimum valid).
    • reference = 'median' and reference = 'mean' both accepted.
  • Normal path:
    • Valid inputs return a quorum evaluation result without throwing, confirming the success branch alongside the failure branches.

Verification Results

npm test -- src/services/fxQuorumEvaluator.test.ts
✅ focused suite passed

npm test
✅ surrounding suite passed

npm run lint
✅ no new warnings or errors

npm run typecheck
✅ no type errors

Acceptance Criteria	Status
Cover the named behavior with focused automated tests, including success and failure paths	✅ Failure branches for k, tolerance, reference plus a valid-input success case
Preserve the existing public contract unless the change includes an explicit compatibility plan	✅ No signature or error-message changes; tests assert current contract
Make error and boundary behavior observable and deterministic	✅ Exact error messages asserted; k = 1 and tolerance = 0 boundaries covered

Closes #1096

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