added Filter method

filter.go

@@ -0,0 +1,16 @@
+package channel
+
+func Filter[T any](source <-chan T, filter func(T) bool) <-chan T {
+	out := make(chan T, cap(source))
+
+	go func() {
+		defer close(out)
+		for value := range source {
+			if filter(value) {
+				out <- value
+			}
+		}
+	}()
+
+	return out
+}