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

candle-pyo3/src/utils.rs

@@ -0,0 +1,6 @@
+use pyo3::exceptions::PyValueError;
+use pyo3::prelude::*;
+
+pub fn wrap_err(err: ::candle::Error) -> PyErr {
+    PyErr::new::<PyValueError, _>(format!("{err:?}"))
+}