feat(isMobilePhone): add Macedonian phone number validation (#2497)

[Sachinsen7]

Added validation regex for Macedonian mobile numbers (locale: mk-MK).

Supports format like +3897XXXXXXX where mobile numbers start with +389 and have 8 digits.

Based on official mobile number format for North Macedonia:
Example valid number: +38970123456

Checklist

• PR contains only related changes; no stray files, etc.
• README updated (not applicable)
• Tests written (if required by maintainers)
• References provided in PR (see above)

[Sachinsen7]

Hey, I’ve created a PR to add Macedonian phone number validation (mk-MK).
All main tests are passing. Please have a look and let me know if any changes are needed
PR: #2571