[graphql/rpc] add tx data loader (#13660)

## Description 

* First impl of [data loader
paradigm](https://github.com/graphql/dataloader) for tx gets to reduce
data layer round trips
* Scalar type for tx digest

## Test Plan 

Manual

---
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### Type of Change (Check all that apply)

- [ ] protocol change
- [ ] user-visible impact
- [ ] breaking change for a client SDKs
- [ ] breaking change for FNs (FN binary must upgrade)
- [ ] breaking change for validators or node operators (must upgrade
binaries)
- [ ] breaking change for on-chain data layout
- [ ] necessitate either a data wipe or data migration

### Release notes

Author: oxade