bug(connections): URL parser stores default port even when URI omits the port

[ZhuchkaTriplesix]

connection_url_parser.dart reads uri.port unconditionally on line 89. If the URI omits the port, uri.port returns the scheme's default port, which is correct for postgresql/postgres (5432), but the code does not explicitly check uri.hasPort. This is fragile if other schemes are added or if Uri behavior changes.

Impact: Persisted port can be 5432 even when not specified, which is mostly harmless but inconsistent with how the form handles omitted ports.

Expected: Only store port when uri.hasPort is true; otherwise leave it null and rely on driver defaults.

Acceptance criteria:

• Use uri.hasPort before assigning uri.port.
• Ensure stored default does not conflict with driver defaults.