Add get_pre_1_wallet_keychains migration helper

[notmandatory]

Description

Add wallet/migration module and get_pre_1_wallet_keychains() 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

This PR replaces bitcoindevkit/bdk#2090 since make more sense to put it in the wallet where it will be easier to export the bindings.

Changelog notice

• Add get_pre_1_wallet_keychains to assist migration from pre-1.0 bdk wallets.

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran just p before pushing

New Features:

• I've added tests for the new feature
• I've added docs for the new feature

[codecov]

Codecov Report

❌ Patch coverage is 90.27778% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.78%. Comparing base (e078db2) to head (80276fc).
⚠️ Report is 15 commits behind head on master.

Files with missing lines	Patch %	Lines
src/wallet/migration.rs	90.27%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #364      +/-   ##
==========================================
+ Coverage   86.75%   86.78%   +0.02%     
==========================================
  Files          25       26       +1     
  Lines        8479     8551      +72     
==========================================
+ Hits         7356     7421      +65     
- Misses       1123     1130       +7     

Flag	Coverage Δ
rust	86.78% <90.27%> (+0.02%)	⬆️

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[thunderbiscuit]

Tested ACK 366ca7a.

[thunderbiscuit]

Part of this PR (rather a sidequest to this PR) could include updating the Migrating from 0.X page on the book of bdk, since this approach is simpler and requires less code, and I think it could simply supercede what we have there (or at least be added as a secondary section/option).

Also would be great to add a small feature page on the Release Guide when we do push the 2.4 section of the Release Guide. I keep track of the features I think should be highlighted here.

[thunderbiscuit]

Two things I'd like to clarify maybe:

1. Can we confirm the versions of bdk this will work for, and add it to the docstrings?
2. Was there a reason to return the descriptor checksum instead of the whole descriptor string?

[notmandatory]

Two things I'd like to clarify maybe:

1. Can we confirm the versions of bdk this will work for, and add it to the docstrings?

The only sqlite tables this function uses is last_derivation_indices and checksums which existed and haven't changed for any pre-1.0 version of bdk. So I'd prefer to leave it as-is and let folks know that this function works for any pre-1.0 version they're on.

2. Was there a reason to return the descriptor checksum instead of the whole descriptor string?

Unfortunately pre-1.0 we did not persist the descriptor string in the sqlite db, all wallet constructors required you pass in your descriptor(s), see: pre-1.0 Wallet docs. All we have in the pre-1.0 sqlite db are the descriptor checksums.

[110CodingP]

Just a nit, feel free to ignore:
Do we need to create an index on the keychain column?

[notmandatory]

Agreed probably don't need it for this test, but I'll leave it since it's copy/paste from pre-1.0 schema sqlite.

[110CodingP]

TACK 366ca7a

Tested by running the following in bdk_wallet@v0.30.2 and bdk_wallet@366ca7a respectively:

use bdk_wallet::rusqlite::{self, Connection};

fn main() -> rusqlite::Result<()> {
    let mut conn = Connection::open("/home/codingp110/pre-1_wallet/.bdk_db.sqlite")?;

    let external_checksum = "1cead456".as_bytes();
    let internal_checksum = "1cead454".as_bytes();

    let result = bdk_wallet::migration::get_pre_1_wallet_keychains(&mut conn)?;
    assert_eq!(result.len(), 2);
    assert_eq!(result[0].keychain, "External");
    assert_eq!(result[0].last_derivation_index, 1337);
    assert_eq!(result[0].checksum, external_checksum);
    assert_eq!(result[1].keychain, "Internal");
    assert_eq!(result[1].last_derivation_index, 68);
    assert_eq!(result[1].checksum, internal_checksum);
    println!("Successful");
    Ok(())
}

and

use bdk::database::SqliteDatabase;
use bdk::database::{BatchOperations, Database};
use bdk::KeychainKind;

fn main() {
    let mut db = SqliteDatabase::new(String::from("./.bdk_db.sqlite"));
    db.set_last_index(KeychainKind::External, 1337).unwrap();
    db.set_last_index(KeychainKind::Internal, 68).unwrap();
    db.check_descriptor_checksum(KeychainKind::External, "1cead456".as_bytes());
    db.check_descriptor_checksum(KeychainKind::Internal, "1cead454".as_bytes());
}

[notmandatory]

Rebased on master branch.

[ValuedMammal]

Code review ACK