Change mj_encode return type to 64-bit (mjtSize)

This supports encoding files larger than 2GB.

PiperOrigin-RevId: 939828697
Change-Id: If60d36c61475ced20b4eb58408ffb37e25bf3db7

python/mujoco/introspect/functions.py

@@ -436,7 +436,7 @@ FUNCTIONS: Mapping[str, FunctionDecl] = dict([
     ('mj_encode',
      FunctionDecl(
          name='mj_encode',
-         return_type=ValueType(name='int'),
+         return_type=ValueType(name='mjtSize'),
          parameters=(
              FunctionParameterDecl(
                  name='s',

python/mujoco/specs.cc

@@ -545,7 +545,7 @@ PYBIND11_MODULE(_specs, m) {
       "encode",
       [](MjSpec& self, std::string filename,
          std::optional<py::object> model,
-         std::optional<std::string> content_type) -> int {
+         std::optional<std::string> content_type) -> mjtSize {
         raw::MjModel* m = nullptr;
         if (model.has_value() && !model->is_none()) {
           auto& wrapper =
@@ -572,8 +572,8 @@ PYBIND11_MODULE(_specs, m) {
         err[0] = '\0';
         const char* ct =
             content_type.has_value() ? content_type->c_str() : nullptr;
-        int nbytes = mj_encode(self.ptr, m, filename.c_str(), ct,
-                               vfs_ptr, err.data(), err.size());
+        mjtSize nbytes = mj_encode(self.ptr, m, filename.c_str(), ct,
+                                   vfs_ptr, err.data(), err.size());
 
         if (vfs_ptr) {
           mj_deleteVFS(vfs_ptr);