Add readExtraAliasEntryOld (tag 20) and readExtraAliasEntry (tag 33)
wire readers so the node can deserialise blocks containing alias
registrations. Without these readers, mainnet sync would fail on any
block with an alias transaction. Three round-trip tests validate the
new readers.
Also apply AX-2 (comments as usage examples) across 12 files: add
concrete usage-example comments to exported functions in config/,
types/, wire/, chain/, difficulty/, and consensus/. Fix stale doc
in consensus/doc.go that incorrectly referenced *config.ChainConfig.
Co-Authored-By: Virgil <virgil@lethean.io>
76488e0beb