fix: latency not correct when set custom url in config

[njzydark]

Currently, there are two main issues with latency testing:

1. When there is a custom testUrl in the configuration file, clicking the speed test does not use the URL from the config file, but instead uses the global configuration
2. The current implementation logic is not strongly bound to testUrl. When fixing the first issue, it causes all identical proxy nodes across different proxy groups to have the same latency time, and their corresponding historical speed test results are also incorrect. This behavior is not as expected

To thoroughly fix this issue, all latency-related logic needs to be strongly bound to testurl

---

Example Config:

  - name: SteamDirect
    type: select
    proxies:
      - DIRECT
      - Proxy
  - name: Home
    type: select
    proxies:
      - DIRECT
      - xray-home
    url: http://wifi.vivo.com.cn/generate_204

before fix:

after fix:

[kunish]

Thanks for the detailed explaination.

[kunish]

This is a relatively large change set. Allow me to find some spare time to review.

[kunish]

LGTM :)