refactor: centralize console worker connections

[EdsonPetry]

What changed

• Introduces a single WorkerConnector abstraction for seed discovery and per-worker polling.
• Routes reconnects and discovered worker URL parsing through the same connection policy.
• Preserves the existing plaintext transport and bare-port CLI behavior.

Why

The console previously opened discovery and worker connections through separate code paths. The next PR needs both paths to apply identical logical-origin and physical-dial behavior for Fabric TLS.

Impact

No intended user-visible behavior change. This is the behavior-neutral base of the console stack.

Validation

• cargo fmt -p datafusion-distributed-console -- --check passed.
• Full test/clippy build was attempted twice but the local build host exhausted file descriptors while compiling aws-sdk-ec2, including with ulimit -n 8192. CI remains the authoritative check.

Stack

1. This PR: centralize console connection creation.
2. Follow-up: support logical TLS worker origins and physical pod dialing.