fix(isCreditCard): anchor Mastercard regex alternation

[leno23]

Summary

• Fix Mastercard regex so ^ and $ bind to the full pattern, not only one branch of the alternation
• Reject partial strings like 5108 that previously matched ^5[1-5][0-9]{2}

Problem

Due to | precedence, the old pattern was parsed as (^5[1-5][0-9]{2}) | ((222...)[0-9]{12}$), allowing any string starting with 51XX–55XX regardless of length.

Test plan

• Added invalid cases: 5108, 5108foo
• Added valid case: 5105105105105100
• npm test — 318 passing

Fixes #2717

Made with Cursor

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (7fdc788) to head (060e01a).

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2718   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          114       114           
  Lines         2587      2587           
  Branches       656       656           
=========================================
  Hits          2587      2587           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.