PyO3: Add optional candle.onnx module (#1282)

* Start onnx integration

* Merge remote-tracking branch 'upstream/main' into feat/pyo3-onnx

* Implement ONNXModel

* `fmt`

* add `onnx` flag to python ci

* Pin `protoc` to `25.0`

* Setup `protoc` in wheel builds

* Build wheels with `onnx`

* Install `protoc` in manylinux containers

* `apt` -> `yum`

* Download `protoc` via bash script

* Back to `manylinux: auto`

* Disable `onnx` builds for linux

.github/workflows/python.yml

@@ -39,6 +39,12 @@ jobs:
           path: ~/.cargo/registry
           key: ${{ runner.os }}-cargo-registry-${{ hashFiles('**/Cargo.lock') }}
 
+      - name: Install Protoc
+        uses: arduino/setup-protoc@v2
+        with:
+            version: "25.0"
+            repo-token: ${{ secrets.GITHUB_TOKEN }}
+
       - name: Install
         working-directory: ./candle-pyo3
         run: |
@@ -46,7 +52,7 @@ jobs:
           source .env/bin/activate
           pip install -U pip
           pip install pytest maturin black
-          python -m maturin develop -r
+          python -m maturin develop -r --features onnx
 
       - name: Check style
         working-directory: ./candle-pyo3