Fix: resolve Qwen3 text encoder loading issues for FP8 and GGUF formats

Description

This PR resolves two separate crashing issues that occur when loading the Qwen3 text encoder in different quantized formats (FP8 Safetensors and GGUF) alongside the Z-Image model.

Issue 1: Missing lm_head.weight in FP8 Safetensors

Error Traceback: Exception: Missing keys: ['lm_head.weight']

Root Cause: Many quantized FP8 checkpoints intentionally drop the lm_head.weight key to save disk space, as it is tied to model.embed_tokens.weight. However, when fast_load_transformers_model is called, mmgp/offload.py performs a strict key check and crashes.