feat(isMobilePhone): add en-TK (Tokelau) validation

[tjt253856563-glitch]

Add en-TK mobile phone validation for Tokelau, accepting prefixes 72, 73 and 74 with 4–7 national digits and an optional +690/690 country code. Update the documented locale list and cover length/prefix boundaries, country-code variants, strict mode, locale arrays, any and locale enumeration.

Numbering reference: ITU Tokelau national numbering plan, communication of 6 December 2015. It lists those mobile prefixes and lengths. This validates number format, not whether a number is assigned.

Refs #1761. This addresses only the Tokelau subtask and does not close the multi-country tracking issue.

Validation on 9ff342479591ca5a43cb30000195bcf55c1bbed9, Windows 11, Node 24.19.0:

• The same three regression tests fail on the baseline with Invalid locale 'en-TK' and pass after the change.
• npm test passes, including Node/ES/browser builds, ESLint and 326 tests.

Checklist

• PR contains only related source, test and documentation changes.
• README locale list updated.
• Tests written and executed.
• Numbering reference provided.

Implementation and test preparation used AI assistance.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (9ff3424) to head (60a1b89).

Additional details and impacted files

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##            master     #2935   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files          114       114           
  Lines         2599      2599           
  Branches       658       658           
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  Hits          2599      2599           

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