Improve slider precision and range clamping, fixes #3206

Add clamping to slider values in both ImGui widgets and mjUI to ensure they remain within the defined min/max ranges, preventing potential floating point inaccuracies from causing values to slightly exceed the bounds.

PiperOrigin-RevId: 902660458
Change-Id: Ia153ae7907f07b890f2b5ac2e3a4be93ecae7bd3

src/experimental/platform/ux/imgui_widgets.cc

@@ -321,7 +321,7 @@ bool ImGui_Slider(const char* name, mjtNum* value, mjtNum min, mjtNum max) {
   float f = *value;
   const bool res = ImGui::SliderFloat(name, &f, min, max);
   if (res) {
-    *value = f;
+    *value = mju_clip(f, min, max);
   }
   return res;
 }