feat: implement modulo operator for numbers with fmod and add test suite

Add num_mod primitive using fmod from math.h to support the % operator on number types. Register the new primitive in the numClass method table. Include a comprehensive test file covering positive, negative, and left-associative modulo cases, plus a divide-by-zero TODO comment in the existing division test.

src/compiler.c

@@ -584,8 +584,6 @@ typedef enum
 static void expression(Compiler* compiler);
 static void statement(Compiler* compiler);
 static void parsePrecedence(Compiler* compiler, Precedence precedence);
-static ObjFn* compileFunction(Parser* parser, Compiler* parent,
-                              TokenType endToken);
 
 typedef void (*ParseFn)(Compiler*);
 

src/primitives.c

@@ -1,3 +1,4 @@
+#include <math.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -119,6 +120,12 @@ DEF_PRIMITIVE(num_divide)
   return (Value)makeNum(AS_NUM(args[0]) / AS_NUM(args[1]));
 }
 
+DEF_PRIMITIVE(num_mod)
+{
+  if (args[1]->type != OBJ_NUM) return vm->unsupported;
+  return (Value)makeNum(fmod(AS_NUM(args[0]), AS_NUM(args[1])));
+}
+
 DEF_PRIMITIVE(num_lt)
 {
   if (args[1]->type != OBJ_NUM) return vm->unsupported;
@@ -256,6 +263,7 @@ void loadCore(VM* vm)
   PRIMITIVE(vm->numClass, "+ ", num_plus);
   PRIMITIVE(vm->numClass, "* ", num_multiply);
   PRIMITIVE(vm->numClass, "/ ", num_divide);
+  PRIMITIVE(vm->numClass, "% ", num_mod);
   PRIMITIVE(vm->numClass, "< ", num_lt);
   PRIMITIVE(vm->numClass, "> ", num_gt);
   PRIMITIVE(vm->numClass, "<= ", num_lte);