Clarify packet framing semantics.
Explicitly state that all body octets must be skipped over when parsing even if not all of them have been interpreted. This may be an odd thing to state, because it may seem obvious, but not every implementation gets that right:
https://tests.sequoia-pgp.org/#Packet_excess_consumption
We see that all versions of GnuPG have trouble with more than ~1k excess bytes, RNP and BouncyCastle with more than ~10k of excess bytes.
If we can rely on implementations getting this right, we can use the compressed data packet to pad messages. See #55 (closed).