Add to rusqlite module the get_pre_1_wallet_keychains migration helper

[notmandatory]

Description

Add to rusqlite module the get_pre_1_wallet_keychains migration to help migrate users from a pre-1.0 bdk sqlite database. This new function returns the last revealed index and checksum value for each keychain it finds.

Notes to the reviewers

Changelog notice

Checklists

All Submissions:

• I followed the contribution guidelines

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

[thunderbiscuit]

Approach ACK. I don't have an opinion as to where it should live per se, although this is mostly related to a pre-1.0 bdk Wallet database, so maybe in bdk_wallet would be closer to its target users? Works either way!

I tested with a local database and I get correct values. Only small comment would be that the string it pulls for the KeychainKind has escaped double quote characters and those are probably not really wanted (see example below).

Pre1WalletKeychain { keychain: "\"External\"", last_derivation_index: 3, checksum: [108, 55, 54, 100, 117, 121, 118, 55] }

[notmandatory]

ah good catch, I didn't notice that with the double quotes, will fix.