chore: rename project from loreg to lorex and add NFA optimization infrastructure

- Rename all source files, headers, and build targets from loreg to lorex
- Add match context struct with pre-allocated state sets for reuse across calls
- Introduce optimization fields in nfa_t: literal prefix/suffix, first character bitmap, alternation dispatch table, anchor flags
- Add benchmark target with -O3 -march=native in Makefile
- Implement bracket_class_t bitmap cache for O(1) character class lookups
- Update README with performance section detailing optimization techniques
- Add coverage/ directory to .gitignore
- Update CHANGELOG to reflect reduced line counts after rename

.gitignore

@@ -6,12 +6,13 @@ build/
 *.dylib
 
 # Binary
-loreg
+lorex
 
 # Coverage
 *.gcov
 *.gcda
 *.gcno
+coverage/
 
 # Profiling
 gmon.out