Add protocol for migration service

Sources/DataRaft/Protocols/MigrationServiceProtocol.swift

@@ -0,0 +1,43 @@
+import Foundation
+
+/// Protocol for managing and running database schema migrations.
+public protocol MigrationServiceProtocol: AnyObject {
+    /// Type representing the schema version for migrations.
+    associatedtype Version: VersionRepresentable
+    
+    /// Provider of encryption keys for the database service.
+    var keyProvider: DatabaseServiceKeyProvider? { get set }
+    
+    /// Adds a migration to be executed by the service.
+    ///
+    /// - Parameter migration: The migration to register.
+    /// - Throws: ``MigrationError/duplicateMigration(_:)`` if a migration with
+    ///   the same version or script URL is already registered.
+    func add(_ migration: Migration<Version>) throws(MigrationError<Version>)
+    
+    /// Runs all pending migrations in ascending version order.
+    ///
+    /// - Throws: ``MigrationError/emptyMigrationScript(_:)`` if a migration
+    ///   script is empty.
+    /// - Throws: ``MigrationError/migrationFailed(_:_:)`` if a script execution
+    ///   or version update fails.
+    func migrate() throws(MigrationError<Version>)
+}
+
+@available(iOS 13.0, *)
+@available(macOS 10.15, *)
+public extension MigrationServiceProtocol where Self: Sendable {
+    /// Asynchronously runs all pending migrations in ascending order.
+    ///
+    /// Performs the same logic as ``migrate()``, but runs asynchronously.
+    ///
+    /// - Throws: ``MigrationError/emptyMigrationScript(_:)`` if a migration
+    ///   script is empty.
+    /// - Throws: ``MigrationError/migrationFailed(_:_:)`` if a script execution
+    ///   or version update fails.
+    func migrate() async throws {
+        try await Task(priority: .utility) {
+            try self.migrate()
+        }.value
+    }
+}