Trace service/endpoint

[lrettig]

This is essential for certain clients (e.g., explorer) to provide state change logs, and it's the only way to know for sure that certain events happened (e.g., token transfers), since contract logs/events aren't always 100% reliable or sometimes don't conform to standards.

From the linked thread:

...state changes are a little different than encoding tx body or logs/events. Ethereum does not include this in the ABI (JSON). The only way to get it is to run a full/archive node in trace mode. We need some sort of API service/endpoint for this.

Originally posted by @lrettig in spacemeshos/pm#134 (comment)

See https://geth.ethereum.org/docs/rpc/ns-debug#debug_tracetransaction