fix(tx_builder)!: make TxBuilder Send safe, remove Clone trait

[notmandatory]

Description

Inspired by discord chat with @stevenroose as a way to make the TxBuilder Send safe.

See his original patch on 1.0.0-beta.5: https://gist.github.com/stevenroose/f7736dfedfaa64bbdbb0da5875df28fc

Notes to the reviewers

I had to remove the Clone trait on TxBuilder but it was only being used in tests.

Changelog notice

• TxBuilder is now Send safe and does not implement the Clone trait

Checklists

All Submissions:

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

New Features:

• I've added tests for the new feature
• I've added docs for the new feature

[notmandatory]

@ValuedMammal you were right, I didn't need the Arc::new(Box::new()) for the test with custom_bip69_ordering. I put it back as it was originally and all still working. This is ready to review.

[stevenroose]

Do we know if there are users using the Clone implementation of TxBuilder? I can see how it might be useful to have for some people..

Otherwise ack 663fb13, changes look good.

Upon further thinking, I think any use of the Clone function can be replaced by a small function re-creating the same builder, I guess.

[notmandatory]

Upon further thinking, I think any use of the Clone function can be replaced by a small function re-creating the same builder, I guess.

We should be fine removing Clone since I don't think anyone is using it and if anyone is there is the work-around to re-creating the builder with the same params. Plus I have gotten feedback from other projects who want TxBuilder to be thread safe so that seems the more valuable thing to do right now.

Long term the goal is to decouple TxBuilder from Wallet and at that point it will be much easier to make TxBuilder cloneable.

[notmandatory]

I moved this back to in-progress, I need to verify bitcoindevkit/bdk-ffi#611 doesn't need TxBuilder to impl Clone.

[evanlinjin]

ACK 663fb13

This makes a lot of sense. I don't see how this will be a problem for ffi, since the TxBuilder struct is only used within the lifetime of the ffi TxBuilder::finish method: https://github.com/bitcoindevkit/bdk-ffi/blob/cf5f714bed70cd7ee09f203f55548fb2a2c478f7/bdk-ffi/src/tx_builder.rs#L371-L399

[notmandatory]

@evanlinjin thanks for checking this for me. You're right that there's no need for .clone() on the bdk_wallet version of TxBuilder in bdk-ffi.