sea-orm integration with sqlite

[dcorral]

Summary

Replaces file-based persistence with SQLite database using sea-orm ORM.

Changes

New database tables:

• mnemonic - encrypted mnemonic storage
• kv_store - LDK persistence (channel manager, payments, swaps, network graph, scorer)
• config - configuration key/value pairs (indexer_url, proxy_url, etc.)
• revoked_token - revoked auth token IDs
• channel_peer - channel peer pubkey/address mapping

Migrated to database:

• Mnemonic (was encrypted file)
• All LDK KVStore data (channel manager, inbound/outbound payments, swaps, scorer)
• Config parameters (synced to files for rust-lightning compatibility)
• Revoked tokens (was flat file)
• Channel peer data (was flat file)
• PSBTs (temporary storage during channel funding)
• Output spender transactions

Architecture:

• Single shared DatabaseConnection via Arc
• SeaOrmKvStore implements rust-lightning's KVStoreSync trait
• Migrations run automatically on startup
• Config stored in DB as source of truth, synced to files for rust-lightning compatibility

[zoedberg]

This is a quick review, will do a more detailed one after the following points have been addressed:

• Why did you put the entities in an entity directory at the project root? If there's no particular reason please generate the entities in a src/database/ directory. Please also check the structure we used in rgb-lib, if possible I would appreciate if we could use the same naming/structure.

• Please create a single init_db migration, it seems overkill to define the DB with multiple separate migrations.

• Please avoid async-std since it's deprecated.

• Please replace the auto-generated README in the migration crate with the one in rgb-lib, I think you can copy that and make only small changes.

• Please do not refactor the test code, the PR should make only the changes necessary for its scope.

• Please drop the src/test/revoked_token_persistence.rs file and just add some checks to the already existing authentication test.

• I see no DB transaction usage, is this because there are no cases where they are required?

• Please explain the purpose of SeaOrmKvStore.

• Please explain or revert the changes to .gitignore.

• Please use the latest version of sea-orm.