Edit username functionality

[nalinbhardwaj]

Challenge: lot of users sign up just to try out the app / without thinking about their username much.

Later when they want to use it more they are sad to discover username is immutable.

Potential solution: allow them to edit username.

Could work as follows:

• Settings has a one-time username edit button
• Editing username creates NameRegistry record for (new username, address). (older username, address) mapping continues to exist as is.
  • This changes one invariant: previously names and addresses are one to one, they won’t be after this. I think it should be relatively straightforward to deal with this though, only using address as source of truth rather than usernames.
• in-app, we can disable the edit username after one time use. some connections like farcaster may need to be reset.
• search continues working for old username and new username.