towards generic method polling and reposito;y; config settings to
filterevents/methods by account address; refactoring some stuff out of
repo and into converter; remove fetcher and instead call
blockchain's FetchContractData directly; finishing tests
* Add constants for TTL and tic for fakeHeader
* Add tic to tend transformer
* Update tests for tend
* Fix string conversion bug in fakes
* Fix tend integration tests after staging rebase
* Add tic to dent transformer
* Update dent tests
* Change integration tests to use hardcoded block timestamp
- Delete header on conflict to prompt data refresh (cascade deletes all
data associated with that block)
- Derive header hash from rpc payload rather than computing it from data
(prevents hash mismatch between blockchain and cache)
