Add multilingual exercise code (#1959)

Replace the exercise pages' Python-only snippets with source-backed implementations for the 13 visible programming languages, and localize reader-facing comments by site language. Zig remains out of scope.

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en/codes/go/chapter_computational_complexity/complexity_exercises_test.go

@@ -0,0 +1,22 @@
+// File: complexity_exercises_test.go
+// Created Time: 2026-08-18
+// Author: Hello Algo Team
+
+package chapter_computational_complexity
+
+import "testing"
+
+func TestComplexityExercises(t *testing.T) {
+	if sumIter(1) != 1 || sumRecur(1) != 1 {
+		t.Fatal("sum functions failed for n = 1")
+	}
+	if sumIter(4) != 10 || sumRecur(4) != 10 {
+		t.Fatal("sum functions failed for n = 4")
+	}
+	if linearLoop(4) != 6 || quadraticLoop(4) != 20 {
+		t.Fatal("complexity loops returned an unexpected value")
+	}
+	if logarithmicLoop(4) != 1 || logarithmicLoop(5) != 1 {
+		t.Fatal("logarithmic loop returned an unexpected value")
+	}
+}