Merge rust-bitcoin#4958: Add remaining units encoders

b787ac2 consensus_encoding: add units encoders (Nick Johnson)

Pull request description:

  Was experimenting with the new encoders and figured I'd throw this up if it saves any busy work. Feel free to close if it will just cause rebase pain.
  
  New encoders for the remaining units crate types which have the legacy encodables trait (minus `BlockHeightInterval` which isn't necessary).


ACKs for top commit:
  apoelstra:
    ACK b787ac2; successfully ran local tests
  tcharding:
    ACK b787ac2


Tree-SHA512: 41ac9dbcef411bb6631fee3a9eac7dfa54d1befcffef9d87b88761ff2a35378cd871b90d9662ec20bf889b7d44891bee2e5de35d9dc39cc88ea1191c1f85603c

Author: apoelstra