Modify Python simulate so that the Reload button works.

Also allow a `Callable[[], [MjModel, MjData]]` to be provided as an argument to `launch` instead of a fixed MjModel/MjData instance. This allows users to customise the behaviour of the Reload button.

Context: https://github.com/deepmind/mujoco/discussions/576#discussioncomment-4161429
PiperOrigin-RevId: 492296268
Change-Id: Ic4b797d2ea8a6967f7e3e7316f2184ea94a86d8b

python/mujoco/simulate.cc

@@ -17,9 +17,7 @@
 #include <string>
 
 #include <simulate.h>
-#include "raw.h"
 #include "structs.h"
-#include <pybind11/detail/common.h>
 #include <pybind11/pybind11.h>
 
 namespace mujoco::python {
@@ -47,8 +45,9 @@ PYBIND11_MODULE(_simulate, pymodule) {
           py::call_guard<py::gil_scoped_release>())
       .def(
           "load",
-          [](mujoco::Simulate& simulate, MjModelWrapper& m, MjDataWrapper& d) {
-            simulate.load("", m.get(), d.get());
+          [](mujoco::Simulate& simulate, const std::string& path,
+             MjModelWrapper& m, MjDataWrapper& d) {
+            simulate.load(path.c_str(), m.get(), d.get());
           },
           py::call_guard<py::gil_scoped_release>())
       .def("applyposepertubations", &mujoco::Simulate::applyposepertubations,