feat: Speeding up loading .safetensors files

[kohya-ss]

• Port from feat: faster MemoryEfficientSafeOpen musubi-tuner#556.
• Refactor to split safetensors utils to a separate python script.

[Copilot]

Pull Request Overview

Refactors safetensors utilities into a separate module to improve code organization and loading performance. This change extracts safetensors-related functionality from the main utils module and optimizes memory-efficient loading with enhanced device synchronization.

Reviewed Changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
library/safetensors_utils.py	New module containing memory-efficient safetensors utilities, enhanced loading functions, and improved device handling
library/utils.py	Removes safetensors utilities and improves code formatting
library/device_utils.py	Adds synchronize_device function and improves clean_memory_on_device type hints
library/custom_offloading_utils.py	Updates to use renamed private functions and adds local utility functions
Multiple training/inference files	Updates imports to use new safetensors_utils module

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