v0.25.0-beta.2

Fix channel subscriber that was blocking sending new requests (#1465)

In RequestMessagesSync subscriber is listening to a feed where all whisper
events are posted. After we received event with a request hash - subscriber will
stop actively consuming messages from a feed, as a subscription channel will
get overflow and whole feed will get blocked.

Some events are posted to a feed before request is sent, so blocked feed results
in blocked sending.

Now we will unsubscribe after relevant event was received, and terminate subscriber
explicitly by timeout.