chore: import upstream snapshot with attribution

doc/source/tune/api/callbacks.rst

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+.. _tune-callbacks-docs:
+
+Tune Callbacks (tune.Callback)
+==============================
+
+See :doc:`this user guide </tune/tutorials/tune-metrics>` for more details.
+
+.. seealso::
+
+    :doc:`Tune's built-in loggers </tune/api/logging>` use the ``Callback`` interface.
+
+
+Callback Interface
+------------------
+
+Callback Initialization and Setup
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. currentmodule:: ray.tune
+.. autosummary::
+    :nosignatures:
+    :toctree: doc/
+
+    Callback
+
+.. autosummary::
+    :nosignatures:
+    :toctree: doc/
+
+    Callback.setup
+
+
+Callback Hooks
+~~~~~~~~~~~~~~
+
+.. autosummary::
+    :nosignatures:
+    :toctree: doc/
+
+    Callback.on_checkpoint
+    Callback.on_experiment_end
+    Callback.on_step_begin
+    Callback.on_step_end
+    Callback.on_trial_complete
+    Callback.on_trial_error
+    Callback.on_trial_restore
+    Callback.on_trial_result
+    Callback.on_trial_save
+    Callback.on_trial_start
+
+
+Stateful Callbacks
+~~~~~~~~~~~~~~~~~~
+
+The following methods must be overridden for stateful callbacks to be saved/restored
+properly by Tune.
+
+.. autosummary::
+    :nosignatures:
+    :toctree: doc/
+
+    Callback.get_state
+    Callback.set_state