BlockService: concurrent block fetch

[kaladinlight]

Overview

synchronous block fetch on un-cached blocks is a bottleneck for tx history fetching

References and additional details

block.go

Acceptance Criteria

• concurrently fetch block details for un-cached blocks

Need By Date

No response

Screenshots/Mockups

No response

Estimated effort

No response

[steel-feel]

Is it still required? If yes, I would like to work on it.