Note that the instance is not const, as it is occasionally useful to be
able to change the select client's fiber after construction. An example
of this use case would be when a select client instance is created for
use with a socket connection (i.e. fd, i.e. fiber), but then, some time
later, needs to be re-used for a different socket connection -
necessitating a fiber switch.
Fiber instance
Note that the instance is not const, as it is occasionally useful to be able to change the select client's fiber after construction. An example of this use case would be when a select client instance is created for use with a socket connection (i.e. fd, i.e. fiber), but then, some time later, needs to be re-used for a different socket connection - necessitating a fiber switch.