Add support for Monaco Postal Code

[danielb7390]

Monaco seems to be a special case inside FR.
Not sure if it should be added to the FR validation or directly to MC or both.

From wikipedia:

Although an independent country, Monaco is part of the French postal code system as if it were a French department, numbered, with codes consisting of 980 and two digits, with 00 being used for deliveries to all physical addresses in the Principality, and 01 to 99 being used for special types of delivery.[3] However the destination country on inbound mail must be specified as "Monaco", not "France".

[Praddy2006]

Looked into this — this looks like it's already been resolved. isPostalCode.js on master already has a dedicated MC locale (MC: /^980\d{2}$/), added in #2682, and the FR pattern already excludes the 98 prefix range, so Monaco codes correctly fail under FR and only pass under MC. That lines up with the note above that inbound mail must specify "Monaco" as the destination, not "France".

Test coverage also confirms this is intentional, not incidental: test/validators.test.js has '98025' in FR's invalid list and the same value in MC's valid list, explicitly proving the France/Monaco boundary is tested.

Given that, this looks safe to close as already resolved by #2682. Happy to open a small follow-up PR to add a bit more edge-case coverage to MC's test block if that'd be useful — let me know if I'm missing something here!