feat: add zero-width character check for email validation

[darkwingpatil]

Summary

Added a new allow_zero_width option to the isEmail validator to detect and reject email addresses containing zero-width characters (U+200B-U+200D, U+FEFF).

Changes

• Added allow_zero_width option to isEmail validator (defaults to true for backward compatibility)
• Implemented regex pattern to detect zero-width characters: [\u200B-\u200D\uFEFF]
• Validation checks both the user part and domain part of email addresses
• Updated README.md documentation to reflect the new option

Motivation

Zero-width characters (invisible Unicode characters) can be used in phishing attacks and to create confusingly similar email addresses. This option allows developers to enable stricter email validation when needed by setting allow_zero_width: false.

Checklist

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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (784e52a) to head (581e7de).

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2648   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          114       114           
  Lines         2572      2576    +4     
  Branches       651       653    +2     
=========================================
+ Hits          2572      2576    +4     

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