Store BDK wallet data in rgb-lib database

[markuslevonyak]

Store the BDK wallet data (its ChangeSet) in rgb-lib's own database instead of a separate bdk_db file, removing the file_store feature.

Motivation

Follow-up to #87: bdk_file_store is a development/testing database not meant for production, and its format breaks across BDK major upgrades. A rescan cannot recover from that, since revealed-but-unpaid invoice addresses have no chain history. #87 (switching to bdk_sqlite) was closed in favor of integrating BDK persistence into rgb-lib's existing database layer: one database technology, no coupling between sea-orm's and BDK's SQLite stacks, room for future non-SQLite backends.

Design

• Relational, mirroring BDK's schema one-to-one (table names singularized, versioning via rgb-lib's migrator): BDK's own persister needs rusqlite, and a serialized-blob approach would be fragile across upgrades. Keeping the schema identical makes future BDK bumps a mechanical diff against upstream's rusqlite_impl.rs.
• Persistence rides rgb-lib's DB transaction: the pool has a single connection and BDK persists happen while a DbTxn is open (sync, broadcast, address reveal), so with single-writer SQLite a separate connection would deadlock. Bonus: BDK and RGB state now commit or roll back atomically.
• Signing and watch-only wallets share one store: BDK persists only the public descriptor (keys live in the in-memory signers), so both produce the identical ChangeSet. The separate bdk_db_watch_only file was a pre-1.0-BDK workaround.

Migration

None: the old bdk_db file is ignored and chain data is rebuilt on the next sync. This one-time break is unavoidable; the new store is what prevents it from recurring.

[codecov]

Codecov Report

❌ Patch coverage is 96.81208% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.25%. Comparing base (fd1aca2) to head (83da955).

Files with missing lines	Patch %	Lines
src/database/bdk.rs	96.48%	18 Missing ⚠️
src/wallet/core.rs	96.77%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #104      +/-   ##
==========================================
+ Coverage   96.24%   96.25%   +0.01%     
==========================================
  Files          24       26       +2     
  Lines       13418    13909     +491     
==========================================
+ Hits        12914    13388     +474     
- Misses        504      521      +17     

Flag	Coverage Δ
rust	96.25% <96.81%> (+0.01%)	⬆️

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[zoedberg]

Thanks a lot for this PR, excellent work!

This is a partial review, will report some stuff here and for some other I will just do a commit on top. Please also lint the code (job is failing)

[zoedberg]

Suggested change

	let mut load_params = BdkWallet::load()
	let mut wallet_params = BdkWallet::load()

let's avoid unnecessary changes to keep the diff small and the blame intact

[markuslevonyak]

You're right. Done.