[Callbacks] Remove double initialization, replace with update_state

[kylesayrs]

Purpose

• Calling initialize twice is a confusing and misleading api. However, in some training pipelines (in this example HF trainer, but potentially others), it may be more convenient to initialize once and then update the state with lazily initialized variables later
• Regardless of whether the HF trainer pathway will be maintained in the future, LLM Compressor should give users the tools to easily integrate with training scripts. HF Trainer is one such integration case which could benefit from a function like this.

Prerequisites

• [Callbacks] Remove pre_initialize_structure #1160

Changes

• Implement update_state which
• Replace the second initialize call in session_mixin with an update_state call