example: Update example_cli and retire old nursery crates

[ValuedMammal]

• Adds two commands init and generate. Loading database doesn't require descriptors
• Replaces send command with psbt (new, sign, and extract). Supports tap key spend
• Uses bdk-coin-select and miniscript plan module

fixes #1469
partially addresses #1462

Notes to the reviewers

Note the example_cli lib now defines the ChangeSet and Anchor type whereas before these were generic

Changelog notice

• Improvements to example_cli that include generating descriptors and creating PSBTs

Checklists

All Submissions:

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

[storopoli]

We could merge this with #1442 and then commit it as a single PR?

If favorable I could rebase #1442 and then you can commit on top of that? Or I can do the opposite as well...

[ValuedMammal]

1442 can be merged anytime and from what I can tell doesn't conflict with this one

[rustaceanrob]

Nice. This cleans things up quite a bit.

[ValuedMammal]

• Rebased onto 17a9850
• For now I'm using bdk_wallet::ChangeSet for the example-cli
• Added back support for single descriptor use
• CI failed to build msrv

[LLFourn]

ConceptACK this looks great.

[evanlinjin]

ACK 771f6b9

A lot better than what we had before. Made the examples a lot more useful.

[ValuedMammal]

Thanks @evanlinjin @LLFourn

We're currently limited to creating PSBTs for wpkh and tr descriptors because I got stuck on trying to add assets/keys for wsh (can still sync and derive addresses though).

[evanlinjin]

@ValuedMammal I think that's fine for now, can add them later