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

introspect/functions.py

@@ -6573,6 +6573,26 @@ FUNCTIONS: Mapping[str, FunctionDecl] = dict([
          ),
          doc='Return max(a,b) with single evaluation of a and b.',
      )),
+    ('mju_clip',
+     FunctionDecl(
+         name='mju_clip',
+         return_type=ValueType(name='mjtNum'),
+         parameters=(
+             FunctionParameterDecl(
+                 name='x',
+                 type=ValueType(name='mjtNum'),
+             ),
+             FunctionParameterDecl(
+                 name='min',
+                 type=ValueType(name='mjtNum'),
+             ),
+             FunctionParameterDecl(
+                 name='max',
+                 type=ValueType(name='mjtNum'),
+             ),
+         ),
+         doc='Clip x to the range [min, max].',
+     )),
     ('mju_sign',
      FunctionDecl(
          name='mju_sign',