Remember compiler options during attach.

Note:
- Move compiler options into `mjsCompiler` struct.
- The compiler options from the attached model are not written by mj_SaveXML.
PiperOrigin-RevId: 689391440
Change-Id: I1d63c146a32f87c737b7a55b64a54b0ffe3aecc9

include/mujoco/mjspec.h

@@ -121,22 +121,15 @@ typedef struct mjsElement_ {       // element type, do not modify
 } mjsElement;
 
 
-typedef struct mjSpec_ {           // model specification
-  mjsElement* element;             // element type
-  mjString* modelname;             // model name
-
-  // compiler settings
+typedef struct mjsCompiler_ {      // compiler options
   mjtByte autolimits;              // infer "limited" attribute based on range
   double boundmass;                // enforce minimum body mass
   double boundinertia;             // enforce minimum body diagonal inertia
   double settotalmass;             // rescale masses and inertias; <=0: ignore
   mjtByte balanceinertia;          // automatically impose A + B >= C rule
-  mjtByte strippath;               // automatically strip paths from mesh files
   mjtByte fitaabb;                 // meshfit to aabb instead of inertia box
   mjtByte degree;                  // angles in radians or degrees
   char eulerseq[3];                // sequence for euler rotations
-  mjString* meshdir;               // mesh and hfield directory
-  mjString* texturedir;            // texture directory
   mjtByte discardvisual;           // discard visual geoms in parser
   mjtByte convexhull;              // compute mesh convex hulls
   mjtByte usethread;               // use multiple threads to speed up compiler
@@ -145,6 +138,18 @@ typedef struct mjSpec_ {           // model specification
   int inertiagrouprange[2];        // range of geom groups used to compute inertia
   int alignfree;                   // align free joints with inertial frame
   mjLROpt LRopt;                   // options for lengthrange computation
+} mjsCompiler;
+
+
+typedef struct mjSpec_ {           // model specification
+  mjsElement* element;             // element type
+  mjString* modelname;             // model name
+
+  // compiler data
+  mjsCompiler compiler;            // compiler options
+  mjtByte strippath;               // automatically strip paths from mesh files
+  mjString* meshdir;               // mesh and hfield directory
+  mjString* texturedir;            // texture directory
 
   // engine data
   mjOption option;                 // physics options