[Scripts] Refactor weight extraction and saving functions

[yuanlehome]

Refactor dtype_byte_size function for clarity and determinism. Introduce _sorted_required_files function to ensure stable sorting of required files. Update extract_mtp_weights and save_safetensors functions for improved type hints and deterministic behavior.

Motivation

由于不保序操作，多次执行 scripts/extract_mtp_weight_from_safetensor.py 脚本保存下来的权重文件不一致

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Modifications

改为保序。

Usage or Command

Accuracy Tests

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[paddle-bot]

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