tapdb: check and error on dirty database version

Add a check during startup to ensure that the database version is not
dirty (i.e., the last migration did not complete successfully). If it is
dirty, the application will exit with an error.

This is done to resolve a bug that would occur when the **latest**
migration failed. In that scenario, the database version would correctly
be marked as dirty and exit with an error. However, under `sqlite`
database backends, when `tapd` was restarted, the dirty database version
would never be checked and `tapd` would start up normally, despite the
database being in a dirty state.
This is due to the check here: https://github.com/lightninglabs/taproot-assets/blob/0ddb08670f59e41e7edb2925a49df18d2124598e/tapdb/sqlite.go#L206-L213
In that scenario, since no migration is needed the migrate library is
never called to perform any potential migration. And since the dirty
check is normally done in the migrate library during a migration, it is
never performed in that scenario.

Author: ViktorT-11

tapdb/migrations.go

@@ -166,12 +166,20 @@ func applyMigrations(fs fs.FS, driver database.Driver, path, dbName string,
 		return err
 	}
 
-	migrationVersion, _, err := sqlMigrate.Version()
+	migrationVersion, dirty, err := sqlMigrate.Version()
 	if err != nil && !errors.Is(err, migrate.ErrNilVersion) {
 		return fmt.Errorf("unable to determine current migration"+
 			"version: %w", err)
 	}
 
+	// If the migration version is dirty, we should not proceed with further
+	// migrations, as this indicates that a previous migration did not
+	// complete successfully and requires manual intervention.
+	if dirty {
+		return fmt.Errorf("database is in a dirty state at version "+
+			"%v, manual intervention required", migrationVersion)
+	}
+
 	// As the down migrations may end up *dropping* data, we want to
 	// prevent that without explicit accounting.
 	latestVersion := opts.latestVersion.UnwrapOr(LatestMigrationVersion)