convert : ability to lazy-load safetensors remotely without downloading to disk ...

convert : ability to lazy-load safetensors remotely without downloading to disk (#12820)

* gguf util : add SafetensorRemote

* fix style

* convert: add --remote option

* convert : allow using lazy remote tensors

It's a bit slow for now since everything is blocking and single-threaded.

* correct metadata.name

* small style fix

* support HF_TOKEN

* convert : use writeable buffer for remote lazy tensors

* convert : fix flake8 lint regarding lamdba assigment

* multithreaded download

* multithread: print debug

* fix style

* Revert "multithreaded download"

This reverts commit 42fc895ace385edc972ad819c76c704aeea61791.

* bring back _get_request_headers

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Co-authored-by: Francis Couture-Harpin <redacted>