Fix domain/hostname generation to comply with RFC 1123

[kingthorin]

Follow-up to PR #1757 where invalid domain names were being generated, particularly affecting non-ASCII locales and special characters in company names.

Problems fixed:

• Ampersands and special characters in company names now properly sanitized
• Non-ASCII locales now generate valid ASCII hostnames (via Punycode)
• Raw Unicode characters no longer leak into URLs
• Invalid Punycode output eliminated

Solution:

• New HostnameHelper class enforces RFC 1123 LDH (Letter-Digit-Hyphen) rules
• HostnameHelper applies IDN.toASCII() for Unicode input, enabling Punycode conversion
• Punycode prefix ("xn--") is preserved during sanitization
• Domain suffixes now route through toAsciiHostname() to preserve multi-label TLDs (e.g., "co.uk")
• All domain generation methods sanitize output to valid RFC 1123 hostnames
• FakerIDN guarantees valid ASCII output, never throws exceptions
• Test patterns updated to accept 2+ label domains

All generated domains are now valid for use with java.net.URL/URI constructors, support multi-label TLDs, and properly handle international domain names via Punycode.

This is a hardening fix with no breaking changes to the public API.

Full disclosure

Claude code was leveraged in part during preparation of this PR.

[what-the-diff]

PR Summary

• Improvements to FakerIDN class:

  • Adjusted certain methods to handle empty or null inputs more gracefully.
  • Added functionality to better process text written in bidirectional languages or with characters that cannot be converted.
  • Added ways to keep track of different processing results.

• Creation of HostnameHelper class:

  • This new class helps with keeping hostnames clean and adhering to specific rules defined in technical document RFC 1123.
  • New methods have been introduced to help with converting and validating hostnames.

• Changes to Company and Internet class:

  • Both classes are now using the newly created HostnameHelper to generate correct and valid domain names and URLs.

• Unit test updates and additions:

  • New tests have been added to confirm the works of HostnameHelper class and it's compliance with the RFC 1123 rules.
  • Old tests in Company class were updated to confirm the validity of the new functionalities.
  • Also, tests for FakerIDN were enhanced to make sure that new fallback mechanisms are working correctly.

• Updated validation patterns for better compliance:

  • Two new patterns were added to ensure that the hostnames and domain names are in line with the rules set out in the RFC 1123 document.
  • Existing tests for web domains and domain names were updated to use these new patterns.

• Enhanced testing for multilingual URLs:

  • Added new tests that ensure web and domain names using Hebrew, Cyrillic, and CJK (Chinese, Japanese, Korean) characters comply with correct rules and do not cause any issues when being used.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 77.90698% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.31%. Comparing base (a947fda) to head (5c0721a).

Files with missing lines	Patch %	Lines
...n/java/net/datafaker/internal/helper/FakerIDN.java	62.85%	4 Missing and 9 partials ⚠️
.../net/datafaker/internal/helper/HostnameHelper.java	84.21%	4 Missing and 2 partials ⚠️
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Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1901      +/-   ##
============================================
- Coverage     92.56%   92.31%   -0.26%     
- Complexity     3573     3598      +25     
============================================
  Files           347      348       +1     
  Lines          7052     7115      +63     
  Branches        675      695      +20     
============================================
+ Hits           6528     6568      +40     
- Misses          365      375      +10     
- Partials        159      172      +13     

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[kingthorin]

Sorry about the churn, it's now ready for review.