feat: add fr-FR license plate validator

[SarthakDudhe]

short description of the changes for this issue:

isLicensePlate: Added support for France (fr-FR), validating French SIV license plates (2 letters, 3 digits, 2 letters, excluding the characters I, O, and U to avoid optical confusion).
Documentation & Tests: Updated README.md to list fr-FR as a supported locale, and added unit tests in test/validators.test.js covering valid (e.g., AB-123-CD, AB123CD) and invalid (e.g., AI-123-BB, ab-123-cd) formats.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (a38f15b) to head (df61f25).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

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##            master     #2806   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files          114       114           
  Lines         2587      2588    +1     
  Branches       656       656           
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+ Hits          2587      2588    +1     

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[tux-tn]

Thank you for your PR

The official ANTS documentation (https://immatriculation.ants.gouv.fr/tout-savoir/numero-logo-et-plaque) (In french) states that the SIV format excludes I, O, and U, and also prohibits the two-letter combination SS:

Une seule association de deux lettres est interdite, SS…

The current regex excludes I/O/U but accepts SS, for example SS-123-AA and AA-123-SS. Could you update the validator and add regression tests covering SS in both letter-pair positions?