Add sign_options argument to Wallet::sign and Wallet::finalize_psbt methods

[thunderbiscuit]

This PR adds an optional SignOptions argument to the methods that can use them on the wallet.

If none is provided, the methods simply use the default values for the SignOptions type (as we did before).

Don't merge just yet, I'll see if I can write a test or two on the Rust side (maybe just for myself).

Changelog notice

Added:
  - New optional argument sign_options on `Wallet::sign` and `Wallet::finalize_psbt` [#650]

[#650]: https://github.com/bitcoindevkit/bdk-ffi/pull/650

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

Bugfixes:

• This pull request breaks the existing API
• I've added tests to reproduce the issue which are now passing
• I'm linking the issue being fixed by this PR

[reez]

ACK 971f2f1

👍 I like this, keeps the API clean and straightforward (while allowing for customization), and is nice that it preserves existing call sites for users that don't require any changes unless they want custom options (other than TapLeavesOptions).

Thanks for adding all those doc strings too!