BIT-LIBPYTHON-2026-19445 Use-after-free of a server-side SSLContext when sni_callback switches contexts

A remote, unauthenticated TLS client can make a server crash or call through a freed pointer if its snicallback assigns a different context to SSLSocket.context the documented way to select a certificate per server name and nothing else keeps the original ssl.SSLContext alive. Typical cases are...