release/0.5.18

What's changed

• Definitions in operator subnamespaces (like List.++.doc) now round-trip.
• Builtin support for Ed25519 signatures.

All PRs since last release

• Update CI badge in README.md by @aryairani in #4710
• stop forgetting to ping @everyone for new releases by @aryairani in #4700
• add export list to Unison.Codebase.Metadata by @aryairani in #4712
• Update copyright by @aryairani in #4718
• remove metadata types from the in-memory branches by @aryairani in #4714
• remove metadata types from the in-memory branches by @aryairani in #4719
• Backticky symbol parsing by @mitchellwrosen in #3525
• Ed25519 builtins for Haskell by @dolio in #4717
• Enable Hash Validation in UCM by @ChrisPenner in #4716
• Local Hash Validation fixups by @ChrisPenner in #4694
• Ensure we tag latest trunk for releases by @ChrisPenner in #4721

Full Changelog: release/0.5.17...release/0.5.18