Support conversion of Qwen3-Embedding models

[iamlemec]

This adds GGUF conversion support for the Qwen3-Embedding class of models and makes pooling work properly by default. I'm not sure how the official Qwen GGUFs were produced, but I'll try to get them updated if this gets merged. More details:

• Though the pre-tokenizer is in fact the same qwen2 as usual, the HF tokenizer adds an EOT token that makes the checksum different from the usual text generation models
• For some reason the tensor names are not prefixed with model. like most other models in this class
• Actually loads the default pooling mode so it works out of the box

[ggerganov]

Thanks for looking into this - it would be great to get this model supported.

[CISC]

Ooops, was a bit trigger happy, forgot convert_hf_to_gguf_update.py...

@iamlemec care to add the model there in a new PR?

Edit: It has to go in pre_computed_hashes (since qwen2 is in models already), which means the entry in convert_hf_to_gguf.py will be moved towards the top as well.

[iamlemec]

@CISC Ah I see, will have that up in a moment. See #15030.