[Single File] Add GGUF support (#9964)

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* Update src/diffusers/quantizers/gguf/utils.py

Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>

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* Update docs/source/en/quantization/gguf.md

Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

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---------

Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

.github/workflows/nightly_tests.yml

@@ -357,6 +357,8 @@ jobs:
         config:
           - backend: "bitsandbytes"
             test_location: "bnb"
+          - backend: "gguf"
+            test_location: "gguf"
     runs-on:
       group: aws-g6e-xlarge-plus
     container: