This PR achieves the following:
1. Improves the exception handling when dialling a peer fails or an unknown error occurs.
2. Add a `Content-Type` header to the `/download` endpoint of `application/octet-stream`, which is [defined by MDN](https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types#types) as meant to be used for "generic binary data (or binary data whose true type is unknown)".
Co-authored-by: Michael Bradley <michaelsbradleyjr@gmail.com>
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