chore: import upstream snapshot with attribution

Sources/CodexBarCore/Logging/CompositeLogHandler.swift

@@ -0,0 +1,40 @@
+import Logging
+
+struct CompositeLogHandler: LogHandler {
+    private var primary: any LogHandler
+    private var secondary: any LogHandler
+
+    init(primary: any LogHandler, secondary: any LogHandler) {
+        self.primary = primary
+        self.secondary = secondary
+    }
+
+    var metadata: Logger.Metadata {
+        get { self.primary.metadata }
+        set {
+            self.primary.metadata = newValue
+            self.secondary.metadata = newValue
+        }
+    }
+
+    var logLevel: Logger.Level {
+        get { self.primary.logLevel }
+        set {
+            self.primary.logLevel = newValue
+            self.secondary.logLevel = newValue
+        }
+    }
+
+    subscript(metadataKey metadataKey: String) -> Logger.Metadata.Value? {
+        get { self.primary[metadataKey: metadataKey] }
+        set {
+            self.primary[metadataKey: metadataKey] = newValue
+            self.secondary[metadataKey: metadataKey] = newValue
+        }
+    }
+
+    func log(event: LogEvent) {
+        self.primary.log(event: event)
+        self.secondary.log(event: event)
+    }
+}