[ZhuchkaTriplesix]

Closes #1307

Problem (redis_connection.dart)

1. The connect had no timeout, unlike PostgreSQL and MySQL (10 s): a host that drops packets held the caller and Test Connection for the OS TCP timeout.
2. When AUTH or PING threw, the failure path only cleared _conn / _command; the socket stayed open, and disconnect() closes only if (wasConnected). Each failed attempt (each Test Connection with a wrong password) left a socket.
3. connect() was not single-flight: two concurrent callers opened two sockets and two SSH tunnels, and the second overwrote the first's connection.

Fix

• The socket is opened by Socket.connect / SecureSocket.connect with connectTimeout (default 10 s, a constructor parameter), then handed to the client with connectWithSocket (already what the TLS path did). AUTH + PING run under the same timeout.
• The failure path destroys the socket it opened.
• connect() shares an in-flight attempt, as in PostgresConnection / MysqlConnection.

Tests (redis_connect_lifecycle_test.dart, with a small RESP server): a wrong password is an authentication failure and the server sees the socket closed; a server that accepts and never answers fails with a timeout error and is closed; two concurrent connects open one connection; a failed attempt can be retried.