Fix bug in simulate noise injection logic.

Noise injection was occurring at every iteration of the physics thread, rather than before every call to `mj_step`, leading to time-step-dependent noise rate.

- Moved the logic from main.cc to a `Simulate::` method, called before `mj_step`.
- Reduced the maximum time-scale slider value back to 4 seconds (recent increase was due to this bug).

PiperOrigin-RevId: 643350296
Change-Id: I96832905e6614f92ac725298b16fcabe64ea1df1

simulate/simulate.h

@@ -86,6 +86,9 @@ class Simulate {
   // add state to history buffer
   void AddToHistory();
 
+  // inject control noise
+  void InjectNoise();
+
   // constants
   static constexpr int kMaxFilenameLength = 1000;
 
@@ -294,7 +297,7 @@ class Simulate {
     {mjITEM_BUTTON,    "Load key",      3},
     {mjITEM_BUTTON,    "Save key",      3},
     {mjITEM_SLIDERNUM, "Noise scale",   5, &this->ctrl_noise_std,  "0 1"},
-    {mjITEM_SLIDERNUM, "Noise rate",    5, &this->ctrl_noise_rate, "0 20"},
+    {mjITEM_SLIDERNUM, "Noise rate",    5, &this->ctrl_noise_rate, "0 4"},
     {mjITEM_SEPARATOR, "History",       1},
     {mjITEM_SLIDERINT, "",              5, &this->scrub_index,     "0 0"},
     {mjITEM_END}