Check if copies of views can be avoided in reductions

[FrancescAlted]

Until now, a copy of a view was needed during reductions: https://github.com/inaos/iron-array/blob/develop/src/reductions/iarray_reduce.c#L1372-L1376. However, the new view implementation should avoid doing the copy. Check that this can be done, and activate that. Also, some benchmarking would be welcome.

[martaiborra]

Checked, copies of views cannot be avoided when computing a reduction since a reduction is applied on the whole array (whole blocks). We should be able to only apply the pre filter to the slice.