fix(identify): check actual port reuse instead of original intent

[ErakhtinB]

When PortUse::Reuse fails and falls back to ephemeral ports, detect this by comparing observed ports with listening ports rather than tracking the original PortUse intent.

Fixes #5820

Description

Notes & open questions

Change checklist

• [x] I have performed a self-review of my own code
• [ ] I have made corresponding changes to the documentation
• [x] I have added tests that prove my fix is effective or that my feature works
• [ ] A changelog entry has been made in the appropriate crates