fix: implement Lua 5.4 patterns (P1-5b) and while pure cond re-evaluation (P1-9)

[esrrhs]

Summary

This PR resolves the two remaining critical open bugs identified during FakeFish integration:

1. Bug 1 (P1-9): Re-evaluate while conditions for impure numeric expressions

   • Problem: When a while condition contained #t (table length), the expression was inferred as T_INT and passed the numeric gate in TryCompileNativeBoolExpr. As a result, FlLenInt was emitted outside the generated native loop, evaluating #t only once before loop entry. Mutating operations like table.remove inside the loop did not update the bound, leading to infinite loops or out-of-bounds nil access.
   • Fix: Added IsPureNativeNumericExp check in c_gen. Only pure expressions (numeric literals, local variables, and pure binary expressions) can be emitted directly as a single native while (cond) loop without external statement dependencies. Impure expressions (e.g. #t) fall back to per-iteration re-evaluation.
   • Verification: Verified on TCC, GCC, and INTERP backends with test_jitbug_while_cond_reval.lua.

2. Bug 2 (P1-5b): Implement standard Lua 5.4 pattern matching for string library

   • Problem: string.find, match, gmatch, and gsub were backed by boost::regex ECMAScript mode. Standard Lua patterns like %.%., %d+, lazy quantifier -, frontier pattern %f[], balanced pattern %b(), and %1-%9 backreferences failed or had incorrect semantics.
   • Fix: Implemented a standalone, zero-dependency byte-pattern matcher (src/native/string/lua_pattern.cpp / lua_pattern.h) ported from Lua 5.4 lstrlib.c. Completely rewired string.find, string.match, string.gmatch, and string.gsub to use the Lua pattern engine.
   • Verification: Added comprehensive test suite test_string_lua_pattern.lua covering classes, quantifiers, captures, nested captures, frontier patterns, balanced matching, and gsub replacement forms. All 54 string unit tests pass across all backends.

Testing

• Full unit test suite passes (test_string*, infer.test_jitbug_while_cond_reval).
• Differential testing against PUC-Rio Lua 5.5 outputs verified on all repro scripts across TCC, GCC, and INTERP backends.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 93.42916% with 32 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.04%. Comparing base (b83f574) to head (e2e730b).

Files with missing lines	Patch %	Lines
src/compile/c_gen.cpp	77.77%	14 Missing ⚠️
src/native/string/lua_pattern.cpp	96.09%	10 Missing ⚠️
src/native/string/native_string.cpp	95.06%	8 Missing ⚠️
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Additional details and impacted files

@@            Coverage Diff             @@
##           master      #24      +/-   ##
==========================================
+ Coverage   87.93%   88.04%   +0.11%     
==========================================
  Files         122      123       +1     
  Lines       24885    25216     +331     
==========================================
+ Hits        21882    22201     +319     
- Misses       3003     3015      +12     

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