Customize tokio runtime for sync operations?

[kylebarron]

Right now we use a hard-coded, global multi-threaded tokio runtime:

obstore/obstore/src/runtime.rs

Lines 8 to 18 in 034f172

	static RUNTIME: GILOnceCell<Arc<Runtime>> = GILOnceCell::new();
	/// Get the tokio runtime for sync requests
	pub(crate) fn get_runtime(py: Python<'_>) -> PyResult<Arc<Runtime>> {
	let runtime = RUNTIME.get_or_try_init(py, || {
	Ok::<_, PyErr>(Arc::new(Runtime::new().map_err(|err| {
	PyValueError::new_err(format!("Could not create tokio runtime. {}", err))
	})?))
	})?;
	Ok(runtime.clone())
	}

Perhaps we should let users customize the parameters of that runtime, and pass in the runtime as a kwarg?

I figure this probably doesn't really matter because the sync operations mean only one will really happen at once?