fix(usockets): safely handle socket reallocation during context adoption

[cirospaciari]

Summary

• Fix use-after-free vulnerability during socket adoption by properly tracking reallocated sockets
• Add safety checks to prevent linking closed sockets to context lists
• Properly track socket state with new is_closed, adopted, and is_tls flags

What does this PR do?

This PR improves event loop stability by addressing potential use-after-free issues that can occur when sockets are reallocated during adoption (e.g., when upgrading a TCP socket to TLS).

Key Changes

Socket State Tracking (internal.h)

• Added is_closed flag to explicitly track when a socket has been closed
• Added adopted flag to mark sockets that were reallocated during context adoption
• Added is_tls flag to track TLS socket state for proper low-priority queue handling

Safe Socket Adoption (context.c)

• When us_poll_resize() returns a new pointer (reallocation occurred), the old socket is now:
  • Marked as closed (is_closed = 1)
  • Added to the closed socket cleanup list
  • Marked as adopted (adopted = 1)
  • Has its prev pointer set to the new socket for event redirection
• Added guards to us_internal_socket_context_link_socket/listen_socket/connecting_socket to prevent linking already-closed sockets

Event Loop Handling (loop.c)

• After callbacks that can trigger socket adoption (on_open, on_writable, on_data), the event loop now checks if the socket was reallocated and redirects to the new socket
• Low-priority socket handling now properly checks is_closed state and uses is_tls flag for correct SSL handling

Poll Resize Safety (epoll_kqueue.c)

• Changed us_poll_resize() to always allocate new memory with us_calloc() instead of us_realloc() to ensure the old pointer remains valid for cleanup
• Now takes old_ext_size parameter to correctly calculate memory sizes
• Re-enabled us_internal_loop_update_pending_ready_polls() call in us_poll_change() to ensure pending events are properly redirected

How did you verify your code works?

Run existing CI and existing socket upgrade tests under asan build

[robobun]

^{Updated 9:28 AM PT - Dec 8th, 2025}

@cirospaciari, your commit 6a87823 is building: #33028