XRPC shouldn't throw on non-200 responses

[mary-ext]

It's frankly annoying to have to handle happy and sad path separately in a try..catch, especially when they can be a quite common thing.

Let's avoid this, we should only throw on exceptional scenarios (e.g. unexpected content-type from #9)

We'll follow a similar response as oazapfts, like so:

const { status, data, headers } = await rpc.get('...');