numeric.c: fix SEGV in int_divmod when argument is not numeric

int_divmod passed an integer mrb_value directly to flo_divmod, which
used mrb_float() to extract the value. In word boxing mode, this caused
a misaligned pointer dereference. Use mrb_ensure_float_type() to safely
convert the integer to float before passing to flo_divmod.

Co-authored-by: Claude <noreply@anthropic.com>

src/numeric.c

@@ -1263,7 +1263,7 @@ int_divmod(mrb_state *mrb, mrb_value x)
 #ifdef MRB_NO_FLOAT
   mrb_raise(mrb, E_TYPE_ERROR, "non integer divmod");
 #else
-  return flo_divmod(mrb, x);
+  return flo_divmod(mrb, mrb_ensure_float_type(mrb, x));
 #endif
 }