Update bdk-ffi to 0.5 (with TxBuilder APIs)

[notmandatory]

Description

Update bdk-ffi to bitcoindevkit/bdk-ffi#123 and add new TxBuilder tests.

Notes to the reviewers

I also fixed tests to use network and addresses for TESTNET to match BlockchainConfig.

The tests must be a bit hacky until we have a way to use REGTEST for our Kotlin tests.

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

[thunderbiscuit]

Looking at this right now. Should the submodule point to a tag on bdk-ffi? The 0.5.0 tag is 8a556d0ba0d5cd499b39dd65ca073229a45ffce2. Just not sure what our "official" procedure is or should be.

[artfuldev]

@thunderbiscuit I was gonna pick that up and complete upgrading to 0.5 but happy to take help.

[thunderbiscuit]

I agree using testnet for the tests is not ideal for now (the wallet will drain rather quickly if we always run tests), but I do think it's good enough for now. I suggested one small change to the error message for the walletTxBuilderBroadcast test. Otherwise everything worked well on my end.

[artfuldev]

I'm yet to upgrade to 0.5 tag which will add 2 new APIs for testing.

[notmandatory]

Until we can get a CI regtest setup (see bitcoindevkit/bdk-ffi#241) I think the best approach is first run the JVM tests locally to get addresses to pre-fund the two testnet wallets for the walletTxBuilderBroadcast and walletTxBuilderDrainWallet tests, then push your changes.

[notmandatory]

After discussing with @thunderbiscuit I commented out the walletTxBuilderDrainWallet test for now, it can be commented out and ran locally until we have a regtest CI setup working.

[artfuldev]

Do we need to add documentation?

[thunderbiscuit]

Tested ACK a67b88a. @artfuldev was there anything else you were wanting to add? Yesterday I think you were saying you wanted to do a few more things. I don't want my ACK to mean "merge" if you're not ready.

[notmandatory]

Rebased. Working on updating the docs.patch then will merge.