fix: properly dispose loop-scoped variables and exit scopes on break

Replace the single `loopBody` index with a `Loop` struct that tracks scope depth, enabling the compiler to emit correct scope-exit code when a `break` statement is encountered inside nested blocks. Also add `WREN_DUMP_COMPILED_CODE` debug flag and new test cases for closures capturing loop variables after break, return inside loops, and nested loop scoping.

test/break/exit_local_scopes.wren

@@ -0,0 +1,18 @@
+for (i in 0..10) {
+  IO.print(i)
+
+  {
+    var a = "a"
+    {
+      var b = "b"
+      {
+        var c = "c"
+        if (i > 1) break
+      }
+    }
+  }
+}
+
+// expect: 0
+// expect: 1
+// expect: 2