Update to bdk-ffi 0.6.0 (remove Blockchain from Wallet)

[notmandatory]

Description

Major API changes from bdk-ffi 0.5.0 -> 0.6.0:

• new Blockchain class constructed from BlockchainConfig
• Wallet sync method requires a Blockchain and optional Progress callback
• Blockchain broadcast method returns no txid value
• new PartiallySignedBitcoinTransaction method to get txid
• TxBuilder.build renamed to TxBuilder.finish to match rust bdk API

Notes to the reviewers

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
• I've updated CHANGELOG.md

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

[notmandatory]

This will be ready to review once bitcoindevkit/bdk-ffi#149 is merged and bdk-ffi release 0.6.0 is tagged.

[thunderbiscuit]

Tested ACK cecf973.