Preserve forwarded client ports in proxy headers middleware

[Kludex]

Summary

• preserve client ports from trusted X-Forwarded-For entries in ProxyHeadersMiddleware
• parse selected forwarded entries conservatively for IPv4 host:port and bracketed IPv6 [host]:port
• keep _TrustedHosts.contains focused on plain host matching by localizing port stripping to get_trusted_client_host()
• cover the behavior with public middleware tests, including a Fix X-Forwarded-For not properly handling ports #2822-style multi-proxy matrix

Inspired by Waitresss reverse-proxy handling, but adapted to Uvicorns existing trust model and localized to X-Forwarded-For client selection.

• Fixes X-Forwarded-For doesn't properly handle ports #2789
• Closes Fix X-Forwarded-For not properly handling ports #2822
• Closes Fix X-Forwarded-For not properly handling ports #2823
• Closes Fix X-Forwarded-For port handling #2820
• Closes Fix X-Forwarded-For not properly handling ports #2809

[github-actions]

📖 Docs preview: https://6b0e881d.uvicorn.pages.dev

[codspeed-hq]

Merging this PR will not alter performance

✅ 24 untouched benchmarks

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_{Comparing fix/x-forwarded-for-port-waitress (67842ad) with main (77843e0)}

[chatgpt-codex-connector]

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[Kludex]

@takeda I gave you co-author given I got some stuff from your PR. Thanks for the contribution. 🙏