Identify bottlenecks of indexer transaction import speed

[dib542]

The transaction import speed can be somewhat slow: in some cases this may be the limiting factor to the usability of the frontend of Duality. If the indexer cannot index transactions as fast as the network generates them (which could be 100s or 1000s per second) then the frontend application state will get further and further out-of-date with the current chain and cause terrible user experiences.

Branches and related issues to this issue should help investigate what can be done to speed up imports.