refactor and cleanup [skip ci]

submodules/Postbox/Sources/PostboxStateView.swift

@@ -0,0 +1,22 @@
+import Foundation
+
+final class MutablePostboxStateView {
+    var state: PostboxCoding?
+    
+    init(state: PostboxCoding?) {
+        self.state = state
+    }
+    
+    func replay(updatedState: PostboxCoding) -> Bool {
+        self.state = updatedState
+        return true
+    }
+}
+
+public final class PostboxStateView {
+    public let state: PostboxCoding?
+    
+    init(_ view: MutablePostboxStateView) {
+        self.state = view.state
+    }
+}