feat: Refactors / moves into individual files, wip.

Sources/ComposableSubscriber/OnFailAction.swift

@@ -4,13 +4,7 @@ import OSLog
 
 public enum OnFailAction<State, Action> {
   case fail(prefix: String? = nil, log: ((String) -> Void)? = nil)
-  case handle((inout State, Error) -> Void)
-
-  @available(macOS 11.0, iOS 14.0, watchOS 7.0, tvOS 14.0, *)
-  @inlinable
-  static func fail(prefix: String? = nil, logger: Logger) -> Self {
-    .fail(prefix: prefix, log: { logger.error("\($0)") })
-  }
+  case operation((inout State, Error) -> Effect<Action>)
 
   @usableFromInline
   func callAsFunction(state: inout State, error: Error) -> Effect<Action> {
@@ -21,10 +15,45 @@ public enum OnFailAction<State, Action> {
       } else {
         return .fail(error: error, log: log)
       }
-    case let .handle(handler):
-      handler(&state, error)
-      return .none
+    case let .operation(handler):
+      return handler(&state, error)
     }
   }
+ 
+  @available(macOS 11.0, iOS 14.0, watchOS 7.0, tvOS 14.0, *)
+  @inlinable
+  static func fail(prefix: String? = nil, logger: Logger) -> Self {
+    .fail(prefix: prefix, log: { logger.error("\($0)") })
+  }
 
+  @inlinable
+  public static func set(
+    _ operation: @escaping @Sendable (inout State, Error) -> Void
+  ) -> Self {
+    .operation(
+      SetAction.operation(operation).callAsFunction(state:value:)
+    )
+  }
+  
+  @inlinable
+  public static func set(
+    _ operation: @escaping @Sendable (inout State, Error) -> Effect<Action>
+  ) -> Self {
+    .operation(
+      SetAction.operation(f: operation).callAsFunction(state:value:)
+    )
+  }
+  
+  @inlinable
+  public static func set(
+    keyPath: WritableKeyPath<State, Error?>,
+    effect: Effect<Action> = .none
+  ) -> Self {
+    .operation(
+      SetAction.optionalKeyPath(
+        keyPath,
+        effect: effect
+      ).callAsFunction(state:value:)
+    )
+  }
 }