Fix WsSession close without notifying Room and Commands not being transmitted

[alexlapa]

Synopsis

According to medea-demo logs after some usage:

1. try_send fails here with SendError::Full (send failed because receiver is full).
2. WsSession can be stopped without notifying Room due to ws::Message stream being finished without emitting ws::Message::Close frame or ws::ProtocolError.

Solution

1. Replace try_send with send.
2. Emit RpcConnectionClosed message in WsSession actor stopped() callback.

Additionally:

1. Cover WsSession with tests.
2. Rework Medea HTTP server tests.
3. Add RpcServer trait and impl it for'Addr<Room>, to make WsSession testable.
4. Split HTTP server configuration to Server::register_data and Server::configure to reuse configuration in tests.

Checklist

• Created PR:
  • [x] In draft mode
  • [x] Name contains WIP: prefix
  • [x] Name contains issue reference
  • [x] Has k:: labels applied
  • [x] Has assignee
• [x] Documentation is updated (if required)
• [x] Tests are updated (if required)
• [x] Changes conform code style
• [x] CHANGELOG entry is added (if required)
• [x] FCM (final commit message) is posted
  • [x] and approved
• [x] Review is completed and changes are approved
• Before merge:
  • [x] Milestone is set
  • [x] PR's name and description are correct and up-to-date
  • [x] WIP: prefix is removed
  • [x] All temporary labels are removed

[alexlapa]

FCM:

Fix WsSession closing without notifying Room and Commands (#76)

- use Addr::send() instead of Addr::try_send() in WsSession when sending messages to Room
- ensure RpcConnectionClosed is sent when WsSession is stopped

Additionally:
- improve WsSession tests
- improve Medea's HTTP server tests