https://rust-lang.github.io/rust-clippy/master/index.html#op_ref

https://rust-lang.github.io/rust-clippy/master/index.html#str_to_string

https://rust-lang.github.io/rust-clippy/master/index.html#needless_lifetimes

Allows Conduit users to join restricted rooms if we are not currently participating

Rejoin room over federation if we are not participating in it; do not include invited users in participating servers calculation

Only 174 errors left!

Remove it from request handler since there's already the context of the
request path, added through TraceLayer.

They are no longer needed in the 2021 edition.