Also implements stack/queue behaviour where if the eyes limit would be
exceeded, either the new eyes cause the oldest eyes to be deleted OR
the new eyes aren't created at all. The default is the first option.
Ensures that if a client becomes idle the segment generator is exited
within a constant amount of time (probably more than this timeout
because of the ASGI server's write buffer and the OS's socket write
buffer, but still constant).
n9k