Fix RpcClient reference leak in Jason (#27)

[evdokimovs]

Part of #27

Synopsis

After RpcClientwas refactored to async_trait usage in #135, RpcClient::on_normal_close starts require one more reference to the RpcClient. Because of it, RpcClient remains alive after Room close.

Solution

1. Return LocalBoxFuture from the RpcClient::on_normal_close instead of async fn usage

2. Add unit tests for this bug

Checklist

• Created PR:
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  • Name contains issue reference
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• Documentation is updated (if required)
• Tests are updated (if required)
• Changes conform code style
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• FCM (final commit message) is posted
  • and approved
• Review is completed and changes are approved
• Before merge:
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[evdokimovs]

Патч с новыми юнит тестами для проверки того, что они падают на мастере. Применять патч нужно на master ветке.

[evdokimovs]

FCM

Fix RpcClient reference leak in Jason (#140, #27)