Allow serialization of Update

[icota]

Description

The rationale behind this is to allow a separate instance of the same wallet be updated on a device that's not necessarily connected. Like a hardware wallet.

A connected device gets the response, serializes it with serde and passes the Update to the air-gapped one.

Depends on bitcoindevkit/bdk#1954

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

[luisschwab]

Closing in favor of #231.

[evanlinjin]

@luisschwab #231 cannot directly replace this PR. Relying on changesets mean that order of updates matter, and for @icota's usecase, it seems they rather not depend on that!

This PR is conceptACK for me, but implementation NACK. The problem is with the serialization of CheckPoint (as mentioned here).

[github-actions]

This pull request has had no activity for 180 days and has been labeled stale. If this work is still in progress or waiting on review, a comment or push will remove the label. PRs with no further activity for 30 days will be closed.

[github-actions]

Closed after 210 days of inactivity. Feel free to reopen if this is still relevant.

[thunderbiscuit]

We should make sure this is closed by a human rather than auto-closed by a bot. This feature would be useful for the bindings in one way or another, so I'm reopening.