Add Hugging Face support and enhance model resolution logic

- Introduced support for Hugging Face API integration, allowing fallback model resolution when Civitai fails.
- Updated configuration to include `HF_TOKEN` and `HF_TOKEN_PATH` for authentication.
- Enhanced model capture logic to differentiate between Civitai and Hugging Face sources.
- Improved error handling for model downloads, providing clearer messages for authentication issues.
- Updated documentation to reflect new environment variables and usage instructions for Hugging Face integration.
- Added tests to validate the new fallback mechanism and ensure robust model resolution.

tests/test_huggingface.py

@@ -0,0 +1,15 @@
+from gpu_rent.huggingface import hf_resolve_url, is_huggingface_url
+
+
+def test_is_huggingface_url():
+    assert is_huggingface_url(
+        "https://huggingface.co/org/model/resolve/main/a.gguf"
+    )
+    assert not is_huggingface_url("https://civitai.red/models/1")
+
+
+def test_hf_resolve_url():
+    assert (
+        hf_resolve_url("bartowski/foo", "bar.gguf")
+        == "https://huggingface.co/bartowski/foo/resolve/main/bar.gguf"
+    )