refactor(server): 优化文件上传配置和MD5计算逻辑

- 移除cloud.js中的异步Promise包装，直接同步计算MD5哈希值
- 在server.js中提取上传大小限制为常量配置
- 统一使用字节单位常量管理文件上传大小限制
- 简化代码结构，提高可读性和维护性

module/cloud.js

@@ -69,11 +69,7 @@ module.exports = async (query, request) => {
     }
   } else {
     if (!fileMd5) {
-      fileMd5 = await new Promise((resolve) => {
-        setImmediate(() => {
-          resolve(crypto.createHash('md5').update(query.songFile.data).digest('hex'))
-        })
-      })
+      fileMd5 = crypto.createHash('md5').update(query.songFile.data).digest('hex')
     }
     fileSize = query.songFile.data.byteLength
   }

server.js

@@ -178,12 +178,15 @@ async function consturctServer(moduleDefs) {
   /**
    * Body Parser and File Upload
    */
-  app.use(express.json({ limit: '500mb' }))
-  app.use(express.urlencoded({ extended: false, limit: '500mb' }))
+  const MAX_UPLOAD_SIZE_MB = 500
+  const MAX_UPLOAD_SIZE_BYTES = MAX_UPLOAD_SIZE_MB * 1024 * 1024
+
+  app.use(express.json({ limit: `${MAX_UPLOAD_SIZE_MB}mb` }))
+  app.use(express.urlencoded({ extended: false, limit: `${MAX_UPLOAD_SIZE_MB}mb` }))
 
   app.use(fileUpload({
     limits: {
-      fileSize: 500 * 1024 * 1024
+      fileSize: MAX_UPLOAD_SIZE_BYTES
     },
     useTempFiles: true,
     tempFileDir: require('os').tmpdir(),