Please, form code into canonical thunk locking mechanism

[Anton-Latukha]

Currently, the code does the thunk locking/unlocking customly. And customly reacts to the locked thread.

All that should be unified. Unification is simple.

MonadThunk needs thunk lock management methods.

[Anton-Latukha]

Maybe the handling of the thunks should be hidden. Aka HNix hierarchy allows to abstract MonadThunk instances from the thunk. So just provide the mechanism to the backend as internal top-level functions.

[Anton-Latukha]

While the handler pattern that often goes also may be overengineering YAGNI, especially at the current moment.
It probably just needs to be with... pattern.

[Anton-Latukha]

Essentially was done.