fix(isFloat): throw on invalid locale instead of an "undefined" separator

[yu2971512385-ui]

Fixes #2862.

The bug

isFloat interpolates the locale separator straight into a RegExp:

const float = new RegExp(`^(?:[-+])?(?:[0-9]+)?(?:\\${options.locale ? decimal[options.locale] : '.'}[0-9]*)?...`);

When options.locale is not a key of decimal, the lookup yields undefined, which stringifies into the pattern as the literal text undefined (the preceding \ + u degrades to a literal u). The compiled separator becomes the 8‑character string undefined, so an unrecognized locale silently accepts nonsense and rejects ordinary decimals — with no error and no fallback:

validator.isFloat('3undefined5', { locale: 'no-such' }); // true  (should not)
validator.isFloat('3.5',         { locale: 'no-such' }); // false (should not)

The fix

Validate options.locale against decimal up front and throw Invalid locale '<locale>' when it is unknown. This mirrors isDecimal (which shares the same decimal map) and the other locale-aware validators (isAlpha, isAlphanumeric, isMobilePhone, isPostalCode, …), which already throw on an invalid locale. Absent/known locales are unaffected.

Tests

Added an isFloat "should error on invalid locale" case alongside the existing isDecimal one. Verified it fails on the unpatched source and passes with the fix; the full suite (npm test) is green.

Checklist

• PR contains only changes related; no stray files, etc.
• README updated (where applicable)
• Tests written (where applicable)
• References provided in PR (where applicable)

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (9ff3424) to head (e5623d6).

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2890   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files          114       114           
  Lines         2599      2601    +2     
  Branches       658       659    +1     
=========================================
+ Hits          2599      2601    +2     

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