[Bug] Make WebSocket teardown safe during connection setup

[GregHolmes]

Follow-up from #104. The generated Listen v1/v2, Speak v1/v2, and Agent v1 WebSocket clients do not have an atomic connection lifecycle: disconnect() can race listener publication and onOpen, leaving a late socket or unresolved connection future.

Scope:

• Define whether disconnect() is terminal or supports reuse.
• Make listener publication, in-flight connection cancellation, onOpen, and retry scheduling safe under that contract.
• Add deterministic race tests for teardown before listener publication, between socket creation and publication, and between onOpen and client-future completion.
• Update all streaming quickstarts only once the generated-client lifecycle is safe.

This is intentionally separate from the SDK-client OkHttp ownership fix in #104.