This package was originally created using reflect to ensure that the
fn to call on every invocation was a func and had receiver params
available to call. But we can remove the reflect package altgether
and alter the package design to take a closure/anon func instead.

This means the caller needs to wrap funcs with receiver args inside
closures, but that is perfectly valid and removes the "slow" reflect
package and still allows the caller to invoke a scheduled func with
any signature of their choosing.