spm: bdk-ffi 2.0

[reez]

Description

Supersedes #297

Notes to the reviewers

Changelog notice

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I have formatted my code with swift-format per .swift-format file

New Features:

• I've added tests for the new feature
• I've added docs for the new feature
• UI changes tested on small, medium, and large devices to ensure layout consistency

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