Consider a different name for `mutate`

[yogurtearl]

the name of the mutate extension could be a bit misleading, since it is returning a new collection with the given modification and not "mutate"ing the existing collection.

In this way, it is similar to the copy method on data classes, so maybe we could change mutate to be copy ?

or some other name that indicates that a new collection is being returned and the existing collection is unmodified.

[i-void]

transform may be

[johannesschaffer]

produce(). The Immer library for javascript uses it