Currently rpc.BlockNumber is marshalled to JSON as a numeric value, which is
wrong because BlockNumber.UnmarshalJSON() wants it to either be hex-encoded
or string "earliest"/"latest"/"pending". As a result, the call chain
rpc.BlockNumberOrHashWithNumber(123) -> json.Marshal() -> json.Unmarshal()
fails with error "cannot unmarshal object into Go value of type string".
- returned headers didn't include mixHash
- returned transactions didn't include signature fields
- empty transaction input was returned as "", but should be "0x"
- returned receipts didn't include the bloom filter
- "root" in receipts was missing 0x prefix