Report a failed first connect once

[Agash]

When the first connection attempt failed with auto-reconnect off, the connection loop and ConnectAsync both finalized the disconnect. Whichever ran first decided the reason Disconnected reported: either the loop's "failed to connect after 1 attempts" or the bare attempt failure. That made ConnectAsync_ConnectionFailedFirstAttempt_NoRetry_RaisesCorrectEvents flaky on the Linux runner, and it failed on master after #47.

ConnectAsync now waits for the loop when the loop is the one that gave up, so Disconnected fires once, with the loop's reason, before ConnectAsync throws. Timeouts and caller cancellation, where the loop may still be retrying, still stop it directly.

The new test holds the loop at the point it gives up, which makes the race deterministic. It failed on every run before this change.