feat(tcp): valid node more strictly

[317787106]

What does this PR do?

• Reuse a shared service-port check during node validation.
• Keep IPv6 normalization independent of service-port handling.
• Improve connection-pool handling of unusable node records and candidates while preserving DNS candidate support.

Why are these changes required?

Node endpoint validation and address handling should apply consistent rules across networking components, and unusable node records should be handled locally during candidate processing.

This PR has been tested by:

• 47 focused tests passed, covering endpoint boundaries, IPv4/IPv6 handling, message validation, connection-pool behavior, and DNS candidates. git diff --check passed.

Follow up

None.

Extra details

IPv6 normalization is independent of service-port handling, and the connection pool continues to support DNS candidates.