Add while loops, GC mark-and-sweep, and malloc block reuse

- Lexer: add INDENT/DEDENT tokens, <, >, : operators, while keyword,
  closing DEDENT emission, include guards
- Parser: add NODE_WHILE with while_loop union, parse while/cond/body
  blocks, include guards
- Eval: add while loop evaluation, GC integration with roots from env,
  debug and gc flags, <, > comparison operators
- GC: implement mark-and-sweep collector with 3 stages (mark roots,
  sweep unmarked, join free blocks)
- Allocator: block reuse via first-fit search with splitting, exponential
  heap growth, NULL check on malloc, include guards, marked field in metadata
- Object: add include guards, fix include to use allocator.h

src/objects/object.h

@@ -1,5 +1,9 @@
+#ifndef JLANG_OBJECT_H
+#define JLANG_OBJECT_H
+
 #include "../memory/allocator.h"
 
+
 #define JLANG_RESOLVE(alloc, offset)                                           \
   ((void *)(((JLANG_memory_allocator *)(alloc))->memory + (offset)))
 
@@ -137,3 +141,5 @@ void obj_print(void *allocator, size_t offset, const char *preffix) {
     break;
   };
 }
+
+#endif