feat: 增加request对body字段的支持

- 实现body字段对json语法，yaml语法的支持的支持
- 新增测试用例login_out.yaml

mocks/v1/auth/login_out.yaml

@@ -0,0 +1,50 @@
+- id: "auth_login_out_001"
+  request:
+    method: "POST"
+    path: "/api/v1/auth/login_out"
+    # 必须包含此 Header 才会匹配
+    headers:
+      Content-Type: "application/json"
+      Authorization: "111"
+      host: "127.0.0.1:8080"
+    body:
+      type: true
+  response:
+    status: 200
+    headers:
+      Content-Type: "application/json"
+      X-Mock-Engine: "Rust-Gemini-v1.2"
+    # 直接内联 JSON 字符串
+    body: >
+      {
+        "code": 0,
+        "data": "退出成功",
+        "msg": "success"
+      }
+  settings:
+    delay_ms: 200 # 模拟真实网络延迟
+- id: "auth_login_out_002"
+  request:
+    method: "POST"
+    path: "/api/v1/auth/login_out"
+    # 必须包含此 Header 才会匹配
+    headers:
+      Content-Type: "application/json"
+      Authorization: "111"
+      host: "127.0.0.1:8080"
+    body:
+      type: false
+  response:
+    status: 200
+    headers:
+      Content-Type: "application/json"
+      X-Mock-Engine: "Rust-Gemini-v1.2"
+    # 直接内联 JSON 字符串
+    body: >
+      {
+        "code": 1,
+        "data": "退出失败",
+        "msg": "success"
+      }
+  settings:
+    delay_ms: 200 # 模拟真实网络延迟