Fix mock onCall behavior for matching expectations

[puneetdixit200]

Purpose (TL;DR) - mandatory

Fixes #2663 by making ordered mock expectations use the method-level call index when selecting onCall() behavior.

Background (Problem in detail) - optional

When separate expectations are configured for the same mocked method, each expectation only sees its own call count. That meant onCall(1) or onCall(2) on later matching expectations fell back to default behavior, so callsFake() returned undefined.

Solution - optional

invokeMethod() now computes the current call index across all expectations for the mocked method and passes it to the selected expectation for the duration of the invocation. getCurrentBehavior() uses that override when present, otherwise it keeps the existing per-stub call-count behavior.

How to verify - mandatory

1. Check out this branch
2. npm install
3. Run:
   • npx mocha --recursive -R dot test/src/mock-test.js --grep "returns callsFake values"
   • npx mocha --recursive -R dot test/src/mock-test.js
   • npx mocha --recursive -R dot "test/src/**/*-test.js" --timeout 10000
   • npm run lint
   • npx prettier --check src/sinon/mock.js src/sinon/stub.js test/src/mock-test.js
   • git diff --check

Not run locally: npm test because npm run build-artifacts currently fails on Windows before tests with Entry module "src\create-sinon-api.js" cannot be external.

Checklist for author

• npm run lint passes
• References to standard library functions are cached.