Fix docstring of mjData.arena. Fixes #1753

PiperOrigin-RevId: 646121139
Change-Id: I46c7fb32b0e705fb3b8301272d7fc55ba0dacd7c

doc/includes/references.h

@@ -179,8 +179,8 @@ struct mjData_ {
   //-------------------- end of info header
 
   // buffers
-  void*   buffer;            // main buffer; all pointers point in it                (nbuffer bytes)
+  void*   buffer;            // main buffer; all pointers point in it            (nbuffer bytes)
-  void*   arena;             // arena+stack buffer                     (nstack*sizeof(mjtNum) bytes)
+  void*   arena;             // arena+stack buffer                               (narena bytes)
 
   //-------------------- main inputs and outputs of the computation
 

include/mujoco/mjdata.h

@@ -207,8 +207,8 @@ struct mjData_ {
   //-------------------- end of info header
 
   // buffers
-  void*   buffer;            // main buffer; all pointers point in it                (nbuffer bytes)
+  void*   buffer;            // main buffer; all pointers point in it            (nbuffer bytes)
-  void*   arena;             // arena+stack buffer                     (nstack*sizeof(mjtNum) bytes)
+  void*   arena;             // arena+stack buffer                               (narena bytes)
 
   //-------------------- main inputs and outputs of the computation
 

introspect/structs.py

@@ -4329,14 +4329,14 @@ STRUCTS: Mapping[str, StructDecl] = dict([
                  type=PointerType(
                      inner_type=ValueType(name='void'),
                  ),
-                 doc='main buffer; all pointers point in it                (nbuffer bytes)',  # pylint: disable=line-too-long
+                 doc='main buffer; all pointers point in it            (nbuffer bytes)',  # pylint: disable=line-too-long
              ),
              StructFieldDecl(
                  name='arena',
                  type=PointerType(
                      inner_type=ValueType(name='void'),
                  ),
-                 doc='arena+stack buffer                     (nstack*sizeof(mjtNum) bytes)',  # pylint: disable=line-too-long
+                 doc='arena+stack buffer                               (narena bytes)',  # pylint: disable=line-too-long
              ),
              StructFieldDecl(
                  name='qpos',