Implement Thompson NFA-based Regular Expressions

[JAi-SATHVIK]

issue #1163

[codecov]

Codecov Report

❌ Patch coverage is 90.95355% with 37 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.28%. Comparing base (3b447b9) to head (7b00548).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
src/regex/stdlib_regex.f90	87.63%	35 Missing ⚠️
test/regex/test_regex.f90	98.41%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1172      +/-   ##
==========================================
+ Coverage   68.66%   69.28%   +0.62%     
==========================================
  Files         408      410       +2     
  Lines       13619    14028     +409     
  Branches     1537     1602      +65     
==========================================
+ Hits         9351     9719     +368     
- Misses       4268     4309      +41     

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[JAi-SATHVIK]

Hi @jalvesz @jvdp1, The "cmake-3.14" job in CI is failing because pip install cmake==3.14.3 requested a version which is no longer available on the PyPI index. can we update the .github/workflows/CI.yml to use cmake==3.14.3.post1?

[JAi-SATHVIK]

Update

I have finalized the core implementation of the pure Fortran regex engine. Here is a summary of what I've completed:

• Correct Shunting-Yard Parsing: Fixed logic bugs in the parser to properly handle parentheses (( and )) and operator precedence during postfix conversion.
• Lexer Anchor Handling: Updated the lexer to accurately handle start (^) and end ($) anchors with correct implicit concatenation logic.
• Accurate Match Reporting: Fixed an off-by-one error in regmatch to ensure correct 1-based match_start indices.
• Safety and Stability: Hardened the engine against out-of-bounds access and memory issues by refactoring eager logical evaluations and utilizing local state management for thread safety.
• Unit Test Integration: Migrated the test suite to the repository's standard test-drive framework, with 10 comprehensive test cases covering literals, character classes, anchors, and alternation.

The engine is now stable, zero-dependency, and ready for your feedback! @arjenmarkus @jvdp1 @jalvesz