fix(daemon): shorten WebSocket serial open timeout

[zackees]

Summary

• reduce WebSocket serial attach open_port(...) timeout from 30s to 3s
• update the comment to explain that the WebSocket localhost path is intentionally shorter than HTTP monitor paths
• add a regression assertion for the 3s timeout constant

Verification

• soldr cargo fmt --all --check
• git diff --check

Note: I did not start another fbuild-daemon Rust test locally because an unrelated soldr cargo test -p fbuild-core usb:: process was already active on this machine and earlier concurrent soldr jobs saturated the local soldr pipe. The source change is limited to a constant/comment plus a simple unit assertion.

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Review details

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 60f24ea1-187b-439f-b15c-7a765aff3fd1

📥 Commits

Reviewing files that changed from the base of the PR and between 4f999cd and 9f6aedc.

📒 Files selected for processing (2)

• crates/fbuild-daemon/src/handlers/websockets.rs
• crates/fbuild-daemon/src/handlers/websockets_tests.rs

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/ws-open-timeout-3s

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