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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codes/swift/chapter_divide_and_conquer/fast_power.swift

@@ -0,0 +1,26 @@
+/**
+ File: fast_power.swift
+ Created Time: 2026-08-18
+ Author: Hello Algo Team
+ */
+
+/* 快速幂 */
+func fastPow(x: Int, n: Int) -> Int {
+    if n == 0 {
+        return 1
+    }
+    let half = fastPow(x: x, n: n / 2)
+    if n % 2 == 0 {
+        return half * half
+    }
+    return half * half * x
+}
+
+@main
+enum FastPower {
+    static func main() {
+        assert(fastPow(x: 7, n: 0) == 1)
+        assert(fastPow(x: 3, n: 5) == 243)
+        assert(fastPow(x: 2, n: 6) == 64)
+    }
+}