Add sugar for allocating N copies of a disposable

[jackfirth]

Using disposable-apply with list to do this is cumbersome, but using it with make-list is subtly wrong: only one value will be allocated and the list will contain that value repeated N times. A simple disposable-repeat procedure would be nice to have.

Use case that spawned this idea is a disposable worker place used in a command line tool where users can control the number of workers with a flag.