Memory leaks cleanup

[DenisBiryukov91]

Describe the release item

There is a series of memory leaks, mostly due to circular dependencies (for example in Runtime) that should be addressed.

[milyin]

Just to keep the history of the issue:
Previous attempt to fix is in #625
The comments about procedure to find leaks and some tool tooling is in https://github.com/milyin/arc-trace

[milyin]

To be resumed after Tokio merging #566