reconnect() holds the pool slot while sleeping between attempts

`Session::reconnect()` sleeps `retry_interval` between passes and walks all endpoints while still holding its pool slot. With defaults (3 endpoints, 3 attempts, 1s interval) the worst case is ~92s, during which concurrent `acquire()` callers get "pool exhausted" — an error that points away from the real cause.

Fix: when the session is handed out from a pool, skip the between-attempt sleeps (the slot is still held, but the hold time drops to the connect+handshake attempts), or shorten them. Standalone sessions keep the current C#-style pacing.

Start by reading Session::reconnect and the pool path that hands sessions to acquire callers, focusing on how pooled versus standalone sessions are identified. Verify that pooled reconnect attempts do not retain the between-attempt sleeps while standalone sessions keep their current pacing, and confirm that concurrent pool acquisition no longer fails because of the delay.

Scritto dal modello di indicizzazione a partire dal testo della issue.