Fix futures not Send

Cargo.lock

Cargo.toml

src/api/client/keys.rs

src/router/mod.rs

src/service/globals/migrations.rs

src/service/pusher/mod.rs

src/service/rooms/event_handler/signing_keys.rs

src/service/sending/appservice.rs

src/service/sending/mod.rs

src/service/sending/send.rs