fix: add overflow check for jump distance in patchJump and emit error on too much code

Add a MAX_JUMP constant set to 2^16 and validate jump distance in patchJump to prevent silent overflow when bytecode exceeds the maximum representable offset. Also remove the TODO comment in endLoop since the forward jump error will be caught by patchJump. Include test cases jump_too_far.wren and loop_too_far.wren to verify the compiler correctly reports "Too much code to jump over." for both conditional and loop constructs.

src/vm/wren_compiler.c

@@ -35,6 +35,10 @@
 // two-byte argument.
 #define MAX_CONSTANTS (1 << 16)
 
+// The maximum distance a CODE_JUMP or CODE_JUMP_IF instruction can move the
+// instruction pointer.
+#define MAX_JUMP (1 << 16)
+
 // The maximum depth that interpolation can nest. For example, this string has
 // three levels:
 //
@@ -1589,7 +1593,8 @@ static void patchJump(Compiler* compiler, int offset)
 {
   // -2 to adjust for the bytecode for the jump offset itself.
   int jump = compiler->bytecode.count - offset - 2;
-  // TODO: Check for overflow.
+  if (jump > MAX_JUMP) error(compiler, "Too much code to jump over.");
+
   compiler->bytecode.data[offset] = (jump >> 8) & 0xff;
   compiler->bytecode.data[offset + 1] = jump & 0xff;
 }
@@ -2848,8 +2853,9 @@ static void loopBody(Compiler* compiler)
 // we know where the end of the loop is.
 static void endLoop(Compiler* compiler)
 {
+  // We don't check for overflow here since the forward jump over the loop body
+  // will report an error for the same problem.
   int loopOffset = compiler->bytecode.count - compiler->loop->start + 2;
-  // TODO: Check for overflow.
   emitShortArg(compiler, CODE_LOOP, loopOffset);
 
   patchJump(compiler, compiler->loop->exitJump);