Reorder _GGUF_QUANT_PREFERENCE so all UD (Unsloth Dynamic) variants
come before standard quants. UD-Q4_K_XL is the default (best
size/quality tradeoff), followed by other UD quants in decreasing
preference order.
For repos without UD variants (e.g., bartowski), falls through to
standard quants starting with Q4_K_M.
Verified with:
- unsloth/Qwen3.5-35B-A3B-GGUF -> UD-Q4_K_XL
- bartowski/Qwen_Qwen3.5-35B-A3B-GGUF -> Q4_K_M
- unsloth/DeepSeek-V3.2-GGUF -> UD-Q4_K_XL (9 shards)
- unsloth/Llama-3.2-1B-Instruct-GGUF -> UD-Q4_K_XL
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