✅ Integration tests & polishing of the existing codebase

[roma-glushko]

Changes

• Covered functionality by integration tests
• Exposed a new param event_buffer_size to control size of the internal Notifier buffer (it's important as we will start missing events on buffer overflow).
• Cleaned NotifierMock.__init__() params
• Handle properly Mutex.lock exceptions. Added more debug statements in event of potential event misses, so misses are not silent
• Stop leaking tokio tasks on event draining
• Fixed rust compilation warnings about dead code and non_local_definitions
• Run tests on PRs via Github Actions