refactor: Use snafu

This should gradtly improve the debugging experience by allowing
tracking backtraces to get more context from the error.
A lot of the touced files here are just cleaning up the old way of
creating errors.

src/core/mod.rs

@@ -14,9 +14,11 @@ pub mod utils;
 
 pub use ::arrayvec;
 pub use ::http;
+pub use ::paste;
 pub use ::ruma;
 pub use ::smallstr;
 pub use ::smallvec;
+pub use ::snafu;
 pub use ::toml;
 pub use ::tracing;
 pub use config::Config;