Renamed the notion of handler classes to plugin classes in the Studio Python API

This change refactors the Python API to use the term "plugins" instead of "handlers" for classes containing decorated handler methods. The term handler is still used for an annotated method of a plugin class that handles a specific message type. Also improved some documentation.

PiperOrigin-RevId: 962150099
Change-Id: I34a8cc410cd784b088605490cfa3baccea5c9e71

python/mujoco/experimental/studio/viewer_handle.py

@@ -16,8 +16,8 @@
 from typing import Any, Callable
 import mujoco
 from mujoco.experimental.studio import endpoints
-from mujoco.experimental.studio import handler_registry
 from mujoco.experimental.studio import messages
+from mujoco.experimental.studio import plugin_registry
 from mujoco.experimental.studio import sim as _sim
 import numpy as np
 
@@ -32,13 +32,13 @@ ShutdownFn = Callable[[float], None]
 
 
 class ViewerHandle:
-  """A handle for interacting with a running Studio application from the sim."""
+  """A handle for interacting with a running viewer application from the sim."""
 
   def __init__(
       self,
       sim_endpoint: endpoints.SimEndpoint,
       *,
-      handlers: list[Any] | None = None,
+      plugins: list[Any] | None = None,
       is_alive_fn: IsAliveFn | None = None,
       shutdown_fn: ShutdownFn | None = None,
   ) -> None:
@@ -46,8 +46,8 @@ class ViewerHandle:
 
     Args:
       sim_endpoint: The endpoint to use for communication with the viewer.
-      handlers: Optional list of handler instances for sim-side processing,
-        which are classes with methods decorated with ``@handler``.
+      plugins: Optional list of plugin instances for sim-side processing, which
+        are classes with methods decorated with ``@handler``.
       is_alive_fn: Optional liveness check; without one the viewer is assumed to
         be running until ``close()`` is called.
       shutdown_fn: Optional launcher-owned shutdown hook, called by ``close()``.
@@ -61,10 +61,10 @@ class ViewerHandle:
     self.data: mujoco.MjData | None = None
     self.step_control: _sim.StepControl | None = None
 
-    # Instantiate handlers from user handlers + framework defaults.
-    all_handlers: list[Any] = list(handlers or [])
-    all_handlers.append(self)
-    self._handlers = handler_registry.HandlerRegistry(all_handlers)
+    # Instantiate handlers from user plugins + framework defaults.
+    all_plugins: list[Any] = list(plugins or [])
+    all_plugins.append(self)
+    self._plugins = plugin_registry.PluginRegistry(all_plugins)
 
   def close(self) -> None:
     """Signals the viewer to exit and waits for it to shut down."""
@@ -128,11 +128,11 @@ class ViewerHandle:
 
     # Process incoming events from the viewer.
     for event in self._sim_endpoint.get_viewer_events():
-      self._handlers.dispatch(event)
+      self._plugins.dispatch(event)
 
     # Process incoming snapshots from the viewer.
     for snapshot in self._sim_endpoint.get_viewer_snapshots():
-      self._handlers.dispatch(snapshot)
+      self._plugins.dispatch(snapshot)
 
     model, data, step_control = self.model, self.data, self.step_control