[Callbacks] Remove EventLifecycle and on_start event (#1170)

## Purpose ##
* Simplify code related to callbacks
  * Remove event lifecycle
    * Callback event lifecycle
    * Optimizer event lifecycle
* Remove the concept of a "start_event", which was originally used
because initialization sometimes requires triggering on_start, and
on_start requires an event in order to get an index and index-related
info
* For now, we create a dummy event on initialization which has an index
of zero
* In the future, all start events will be triggered by events (never
initialize) and all event events will be triggered by events or
finalization

## Prerequisites ##
* #1160

## Changes ##

* Instead of using event lifecycle as a proxy, pass events to modifiers
directly
```python3
- self._check_setup_event_lifecycle(event_type)
+ event = Event(event_type=event_type)
- for event in self.event_lifecycle.events_from_type(event_type):
+ for mod in self.modifiers:
     data = mod.update_event(state=self.state, event=event, **kwargs)
```
* This was originally needed for optimizer event lifecycle, that is now
removed
* Make silent noops into errors
```python3
  if not self.initialized_:
-     return
+     raise RuntimeError("Cannot update an uninitialized modifier")

```
* Remove `check_initialized`, which was used to allow for checking in
situations which required double initialization

Signed-off-by: Kyle Sayers <[email protected]>

Author: kylesayrs

src/llmcompressor/core/__init__.py

@@ -1,10 +1,4 @@
-from llmcompressor.core.events import (
-    CallbacksEventLifecycle,
-    Event,
-    EventLifecycle,
-    EventType,
-    OptimizerEventLifecycle,
-)
+from llmcompressor.core.events import Event, EventType
 from llmcompressor.core.lifecycle import CompressionLifecycle
 from llmcompressor.core.model_layer import ModelParameterizedLayer
 from llmcompressor.core.session import CompressionSession
@@ -20,9 +14,6 @@
 __all__ = [
     "Event",
     "EventType",
-    "EventLifecycle",
-    "CallbacksEventLifecycle",
-    "OptimizerEventLifecycle",
     "State",
     "Data",
     "Hardware",

src/llmcompressor/core/events/__init__.py

@@ -8,14 +8,5 @@
 """
 
 from .event import Event, EventType
-from .event_lifecycle import EventLifecycle
-from .lifecycle_callbacks import CallbacksEventLifecycle
-from .lifecycle_optimizer import OptimizerEventLifecycle
 
-__all__ = [
-    "Event",
-    "EventType",
-    "EventLifecycle",
-    "CallbacksEventLifecycle",
-    "OptimizerEventLifecycle",
-]
+__all__ = ["Event", "EventType"]