eth_feeHistory validation of different clients before 1559

[juanfranblanco]

There has been some issues with the RPC implementation with different inputs and outputs formats. If we could validate all of the clients before going live, and have further eyes on this, it will be great.

Clients tested:

Geth
Input: blockCount is not in Hex, this pull fixes it ethereum/go-ethereum#23239
Output: OldestBlock is not in Hex

Besu
Corrected on hyperledger/besu#2517
Seems ok.

**Open Ethereum / Parity"
Seems ok.

Others?

[lightclient]

It appears that all the EL clients have resolved this issue with eth_feeHistory. Going forward, yes, we need to be vigilant that clients behave the same before going live. We've done some work since this issue was posted to be able to catch issues early, on all clients, automatically. This is done by running rpc-compat simulator in hive: https://github.com/ethereum/hive/tree/master/simulators/ethereum/rpc-compat