No longer modify control vector in-place, add mju_clip.

- Never modify `d->ctrl`:
  - `ctrl` values which are outside their respective `ctrlrange` are clamped internally, but `d->ctrl` itself is unmodified.
  - Similarly, if `mjWARN_BADCTRL` is raised (NaNs or huge values), `ctrl` is cleared internally, but `d->ctrl` itself is unmodified.
- `mjWARN_BADCTRL` is no longer raised for `d->ctrl` values that are larger in absolute value than `mjMAXVAL`, if clamping makes them smaller than that.
- Added `mju_clip()` utility function.
- Added missing warning string for `case mjWARN_BADCTRL`.

PiperOrigin-RevId: 459025950
Change-Id: Ifbf974f9c02c3d70afdaa3114018fc81dfd746d3

src/engine/engine_util_misc.h

@@ -69,6 +69,9 @@ MJAPI mjtNum mju_min(mjtNum a, mjtNum b);
 // max function, single evaluation of a and b
 MJAPI mjtNum mju_max(mjtNum a, mjtNum b);
 
+// clip x to the range [min, max]
+MJAPI mjtNum mju_clip(mjtNum x, mjtNum min, mjtNum max);
+
 // sign function
 MJAPI mjtNum mju_sign(mjtNum x);