regex surface API

[hackwaly]

Summary

This PR introduces a full surface regex API for both string and bytes, built on top of the existing regex engine and parser infrastructure.

What changed

• Added compile entrypoints:
  • Regex::new(StringView) -> Regex raise
  • BytesRegex::new(StringView) -> BytesRegex raise
• Added escaping helpers:
  • Regex::escape(StringView) -> StringView
  • BytesRegex::escape(StringView) -> StringView
• Added high-level regex operations for both Regex and BytesRegex:
  • find
  • replace_by
  • split
• Renamed internal package internal/regex_parser to internal/regex_syntax.
• Added internal/regex_syntax::escape with dedicated tests.
• Expanded string/bytes README regex sections with syntax coverage, constraints, and runnable examples.

Semantics and notes

• APIs are marked experimental/internal (subject to change).

Tests

• Added comprehensive tests for:
  • compile success/failure cases
  • non-capturing and named groups
  • replace/split behavior (including zero-width edge cases)
  • iterator progress/exhaustion for find
  • regex escaping behavior
• CI stable checks pass across Linux/macOS/Windows.

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[coveralls]

Pull Request Test Coverage Report for Build 2638

Details

• 83 of 91 (91.21%) changed or added relevant lines in 6 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.7%) to 96.711%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
bytes/regex.mbt	5	6	83.33%
string/regex.mbt	6	7	85.71%
bytes/regex_methods.mbt	29	32	90.63%
string/regex_methods.mbt	33	36	91.67%

Totals
Change from base Build 2631:	0.7%
Covered Lines:	12086
Relevant Lines:	12497

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💛 - Coveralls

[devin-ai-integration]

Devin Review found 1 potential issue.

View 6 additional findings in Devin Review.

[devin-ai-integration]

Devin Review found 1 new potential issue.

View 10 additional findings in Devin Review.