text: Title: MEXC wrong signature for broker endpoints
  Body: ### Operating System
  
  _No response_
  
  ### Programming Languages
  
  JavaScript
  
  ### CCXT Version
  
  latest
  
  ### Description
  
  There is some mistake in `sign` function for MEXC POST/PUT/DELETE private **broker** endpoints (https://mexcdevelop.github.io/apidocs/broker_en/#create-a-sub-account and others from this page). We need to put `timestamp/recvWindow/signature` parameters in URL however other parameters should be in Request body.
  
  In the current implementation I get error:
  ```
  fetch Request:
   mexc POST https://api.mexc.com/api/v3/broker/sub-account/virtualSubAccount?subAccount=Test1test&note=Test&timestamp=1737462608011&recvWindow=5000&signature=xxx 
  RequestHeaders:
   {
    'X-MEXC-APIKEY': 'xxx',
    source: 'CCXT',
    'Content-Type': 'application/json'
  } 
  RequestBody:
   undefined 
  
  handleRestResponse:
   mexc POST https://api.mexc.com/api/v3/broker/sub-account/virtualSubAccount?subAccount=Test1test&note=Test&timestamp=1737462608011&recvWindow=5000&signature=xxx
  ResponseHeaders:
   {
    'Access-Control-Expose-Headers': 'x-cache',
    'Akamai-Grn': 'xxx',
    'Cache-Control': 'max-age=0, no-cache, no-store',
    Connection: 'keep-alive',
    'Content-Length': '81',
    'Content-Type': 'application/json',
    Date: 'Tue, 21 Jan 2025 12:30:08 GMT',
    Expires: 'Tue, 21 Jan 2025 12:30:08 GMT',
    Pragma: 'no-cache',
    'Server-Timing': 'cdn-cache; desc=MISS, edge; dur=282, origin; dur=20, ak_p; desc="xxx";dur=1',
    'Strict-Transport-Security': 'max-age=63072000; includeSubdomains; preload',
    'X-Cache': 'NotCacheable from child'
  } 
  ResponseBody:
   {"success":false,"code":33333,"msg":"Parameter error","data":null,"_extend":null} 
  ```
  
  But it works fine if I put `subAccount` and `note` in request body (tested). Can you please fix it in a best way?
  
  ### Code
  
  
  