feat: 新增 UDP checker，支持自定义 payload 请求-响应探测与断言

基于 Bun connected UDP socket 实现通用 UDP 拨测能力：
- 支持 text/hex/base64 payload 编码与独立 responseEncoding 响应视图
- 支持 responded、response、responseSize、sourceHost、sourcePort、maxDurationMs 专属 expect
- 单 datagram 发送，仅断言首个 UDP 响应 datagram
- 通过 maxResponseBytes 和 flags.truncated 进行响应大小限制与截断保护
- payload 可选，省略时发送空 datagram
- 自包含模块结构（types/schema/validate/expect/encoding/execute）
- 新增 741 tests（含 unit、execute 集成、expect 和编码 roundtrip），全部通过

tests/server/checker/runner/udp/expect.test.ts

@@ -0,0 +1,120 @@
+import { describe, expect, it } from "bun:test";
+
+import {
+  checkResponded,
+  checkResponseSize,
+  checkResponseText,
+  checkSourceHost,
+  checkSourcePort,
+} from "../../../../../src/server/checker/runner/udp/expect";
+
+describe("checkResponded", () => {
+  it("responded=true 期望 true → 匹配", () => {
+    const result = checkResponded(true, true);
+    expect(result.matched).toBe(true);
+    expect(result.failure).toBeNull();
+  });
+
+  it("responded=false 期望 true → 不匹配", () => {
+    const result = checkResponded(false, true);
+    expect(result.matched).toBe(false);
+    expect(result.failure!.kind).toBe("mismatch");
+    expect(result.failure!.phase).toBe("responded");
+  });
+
+  it("responded=false 期望 false → 匹配", () => {
+    const result = checkResponded(false, false);
+    expect(result.matched).toBe(true);
+    expect(result.failure).toBeNull();
+  });
+
+  it("responded=true 期望 false → 不匹配", () => {
+    const result = checkResponded(true, false);
+    expect(result.matched).toBe(false);
+    expect(result.failure!.kind).toBe("mismatch");
+    expect(result.failure!.phase).toBe("responded");
+  });
+});
+
+describe("checkResponseSize", () => {
+  it("size=4 gte=4 → 匹配", () => {
+    const result = checkResponseSize(4, { gte: 4 });
+    expect(result.matched).toBe(true);
+    expect(result.failure).toBeNull();
+  });
+
+  it("size=2 gte=4 → 不匹配，phase=responseSize", () => {
+    const result = checkResponseSize(2, { gte: 4 });
+    expect(result.matched).toBe(false);
+    expect(result.failure!.kind).toBe("mismatch");
+    expect(result.failure!.phase).toBe("responseSize");
+  });
+
+  it("size=10 lt=20 → 匹配", () => {
+    const result = checkResponseSize(10, { lt: 20 });
+    expect(result.matched).toBe(true);
+  });
+
+  it("size=5 equals=5 → 匹配", () => {
+    const result = checkResponseSize(5, { equals: 5 });
+    expect(result.matched).toBe(true);
+  });
+});
+
+describe("checkResponseText", () => {
+  it("单条 contains 匹配", () => {
+    const result = checkResponseText("PONG", [{ contains: "PONG" }]);
+    expect(result.matched).toBe(true);
+    expect(result.failure).toBeNull();
+  });
+
+  it("单条 contains 不匹配，phase=response", () => {
+    const result = checkResponseText("PING", [{ contains: "PONG" }]);
+    expect(result.matched).toBe(false);
+    expect(result.failure!.kind).toBe("mismatch");
+    expect(result.failure!.phase).toBe("response");
+  });
+
+  it("多条规则全部匹配", () => {
+    const result = checkResponseText("hello world", [{ contains: "hello" }, { match: "^hello" }]);
+    expect(result.matched).toBe(true);
+    expect(result.failure).toBeNull();
+  });
+
+  it("多条规则第二条失败 → 不匹配", () => {
+    const result = checkResponseText("hello world", [{ contains: "hello" }, { match: "^world" }]);
+    expect(result.matched).toBe(false);
+    expect(result.failure!.phase).toBe("response");
+    expect(result.failure!.path).toBe("response[1]");
+  });
+});
+
+describe("checkSourceHost", () => {
+  it("equals 匹配", () => {
+    const result = checkSourceHost("127.0.0.1", { equals: "127.0.0.1" });
+    expect(result.matched).toBe(true);
+    expect(result.failure).toBeNull();
+  });
+
+  it("equals 不匹配", () => {
+    const result = checkSourceHost("10.0.0.1", { equals: "127.0.0.1" });
+    expect(result.matched).toBe(false);
+    expect(result.failure!.kind).toBe("mismatch");
+    expect(result.failure!.phase).toBe("sourceHost");
+  });
+});
+
+describe("checkSourcePort", () => {
+  it("equals 匹配", () => {
+    const result = checkSourcePort(9000, { equals: 9000 });
+    expect(result.matched).toBe(true);
+    expect(result.failure).toBeNull();
+  });
+
+  it("equals 不匹配", () => {
+    const result = checkSourcePort(8080, { equals: 9000 });
+    expect(result.matched).toBe(false);
+    expect(result.failure!.kind).toBe("mismatch");
+    expect(result.failure!.phase).toBe("sourcePort");
+  });
+});