feat(service-discovery): 稳定应用级服务发现使用的元数据key

[Alanxtl]

背景

应用级服务发现集合 listener key 之前依赖 services.String()，相同应用集合在不同遍历顺序下可能生成不同 key，导致 listener 复用不稳定。

改动内容

• 将 services.String() 替换为排序后的稳定 application set key。

价值

• 提升应用级服务发现 listener key 的稳定性，避免相同应用集合产生不同订阅 key。

Checklist

• I confirm the target branch is develop
• Code has passed local testing
• I have added tests that prove my fix is effective or that my feature works

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 52.53%. Comparing base (60d1c2a) to head (0aa91ec).
⚠️ Report is 814 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3362      +/-   ##
===========================================
+ Coverage    46.76%   52.53%   +5.76%     
===========================================
  Files          295      492     +197     
  Lines        17172    37878   +20706     
===========================================
+ Hits          8031    19898   +11867     
- Misses        8287    16374    +8087     
- Partials       854     1606     +752     

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