Instead of patching BlockHeader or BlockBody codec
each time it get additional optional fields,
this PR make the rlp codec automatically handle
optional fields. Thus rlp codec overloading of
EthBlock, BlockHeader, and BlockBody can be removed.
Using exception in rlp.append turn out creates more problem than it solve.
`blockHash` operation is literally everywhere in nimbus-eth1, nimbus-eth2, and fluffy-code.
The compiler begins to complain about unlisted exception.
Rlp bytes coming from network and test vectors already verified by the decoder.
So, any invalid optional fields of blockheader that come into rlp.append means
programming error. Assertion will be more apropiate in this situation and less problematic.
including:
- fix rlp.append of BlockHeader
- add tests for rlp.readRecordType of BlockBody
- add tests for rlp.append of BlockHeader
- add tests for EthBlock roundtrip