Fix async listener for UNIX domain socket PostgreSQL connections

[devin-ai-integration]

Fixes the PostgreSQL async LISTEN/NOTIFY connection when using UNIX domain socket connection URLs (e.g. postgresql+asyncpg:///prefect?host=/tmp/.SOSHUB&port=25432).

SQLAlchemy's make_url() places host and port in the query parameters dict for these URLs rather than the standard .host/.port attributes. The existing code only checked the URL authority attributes, so both were None for socket-style URLs, causing the listener connection to fail.

The fix falls back to query params when the standard URL attributes are not set.

Review checklist for humans

• Verify int(port) cast is safe for both paths: asyncpg_dsn.port (already int) and query.get("port") (returns str). The if port: guard prevents int(None).
• Consider whether query.get("host") could return a tuple for repeated keys in SQLAlchemy's immutabledict — unlikely but possible edge case.
• Confirm no other query params (e.g. sslmode) need similar treatment for socket connections.

Closes #20742

Checklist

• This pull request references any related issue by including "closes <link to issue>"
• If this pull request adds new functionality, it includes unit tests that cover the changes
• If this pull request removes docs files, it includes redirect settings in mint.json.
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Link to Devin run

https://app.devin.ai/sessions/2a11bbb3200e4b979560213735485e55

Requested by: @zzstoatzz

[devin-ai-integration]

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[codspeed-hq]

Merging this PR will not alter performance

✅ 2 untouched benchmarks

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_{Comparing devin/1771441135-fix-unix-socket-pg-listener (64ab0e0) with main (0f5c339)}