fix(isByteLength): handle unpaired surrogates instead of throwing

[sarathfrancis90]

isByteLength throws a URIError instead of returning a boolean when the input contains an unpaired surrogate:

validator.isByteLength('\uD835', { max: 3 }); // URIError: URI malformed
validator.isEmail('\uD835');                  // URIError (isEmail runs the local part through isByteLength)

encodeURI() rejects unpaired surrogates, so the byte-count line blows up. Every other validator just returns false on this kind of input, so the throw is both surprising and a small hazard when validating untrusted strings.

The fix replaces unpaired surrogates with U+FFFD before encoding — that's the same substitution a UTF-8 encoder makes (3 bytes), so the byte count stays correct and valid surrogate pairs are left exactly as they were. I added a regression test for both isByteLength and isEmail; the full suite passes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (7fdc788) to head (9492b89).

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2742   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          114       114           
  Lines         2587      2595    +8     
  Branches       656       659    +3     
=========================================
+ Hits          2587      2595    +8     

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