Write multi-thread code to deal with multiple flushing operations

[jorgeantonio21]

Atm, we only deal with insert operations on the DB. We might as well write the flush logic to deal with multiple threads, to improve efficiency of runtime execution. @vadim-frolov suggested we use connection pools for it:

https://docs.rs/r2d2/latest/r2d2/index.html

Further discussion might be needed for update and delete operations.

[benjaminbollen]

yes to this issue;

but on update and delete: update and delete operations are not CALM https://arxiv.org/abs/1901.01930.

So I would leave implementing them for when we have enough structure on the commitments of (inserted / appended) records, bootstrapped a peer-2-peer network, and possibly even the full counterfactual proofs, because all these components may weigh in on how we want to think about not-CALM operations (and where our optimization focus will lie)

I would put these ops on ice until much more has been built out

[benjaminbollen]

I am not sure we should multithread the connection to the anchorDB; rather improving the runtime; and multithreading different tasks first might be more important first; we will want to handle multiple concurrent packages soon, then sharing the anchorDB connection will be important; putting this on ❄️ ice for now