Passing a single transport instance to MtCuteClient caused the FakeTLS
context to be reused across reconnects and secondary DC connections,
resulting in "Invalid TLS header" errors. Use a factory function so each
connection gets a fresh MtProxyTcpTransport.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NhaENbg5p8KWu8TBpHvHvc