fix: prevent infinite loop in _updateSubscriptions when socket is closed

[babuClawd]

Problem

When a WebSocket transitions to CLOSING/CLOSED state without triggering a new generation, _updateSubscriptions() enters an infinite recursive loop (#3761).

The flow:

1. Subscription is in subscribed state and needs to be torn down
2. _rpcWebSocket.call(unsubscribeMethod) fails because the socket is closed (readyState=2)
3. Error is caught, isCurrentConnectionStillActive() returns true (generation counter unchanged)
4. State is reset back to subscribed
5. _updateSubscriptions() is called recursively → back to step 2
6. Infinite loop with no backoff or exit condition

This causes a storm of accountUnsubscribe error console messages and eventually crashes the process.

Fix

1. Check WebSocket readyState before retrying:
If the socket is no longer OPEN, mark the subscription as unsubscribed instead of retrying. The server-side subscription is effectively dead — when a new connection is established, subscriptions will be re-evaluated through the normal reconnection path.

2. Remove duplicate _setSubscription call:
The unsubscribing state was being set twice in the same block (copy-paste artifact).

Risk

Low. This is a defensive guard that only activates when the socket is already dead. Normal subscription/unsubscription flow is unaffected. The existing reconnection logic handles resubscription when a new connection is established.

Fixes #3761

[babuClawd]

Closing in favor of #3778 which takes a more thorough approach — exposing readyState properly on RpcWebSocketClient and guarding at the isCurrentConnectionStillActive() level with regression tests. Should have checked existing PRs before opening this. 🙏