feat: implement Opus decoder runtime checks and add tests for decoder functionality

tests/decoder.test.ts

@@ -0,0 +1,33 @@
+import process from "node:process";
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+beforeEach(() => {
+  process.env = {
+    ...process.env,
+    DISCORD_TOKEN: "token",
+    NODE_ENV: "test",
+  };
+  vi.resetModules();
+});
+
+describe("shouldEnableDefaultOpusDecoder", () => {
+  it("disables default decoder on Bun when native opus is unavailable", async () => {
+    const { shouldEnableDefaultOpusDecoder } = await import(
+      "../src/recorder/decoder"
+    );
+
+    expect(
+      shouldEnableDefaultOpusDecoder({ isBun: true, canLoadNativeOpus: false }),
+    ).toBe(false);
+  });
+
+  it("enables default decoder when native opus is available", async () => {
+    const { shouldEnableDefaultOpusDecoder } = await import(
+      "../src/recorder/decoder"
+    );
+
+    expect(
+      shouldEnableDefaultOpusDecoder({ isBun: true, canLoadNativeOpus: true }),
+    ).toBe(true);
+  });
+});