Use inline iterators to avoid copying
Unfortunately inline iterator chaining is broken: https://github.com/nim-lang/Nim/issues/4516
As a workaround, closures are currently used

Occurrences:
- https://github.com/mratsim/Arraymancer/blob/8551acb3561878c6effc04b5f39ee211e5f36031/src/arraymancer/operators_blas_l1.nim#L58
- https://github.com/mratsim/Arraymancer/blob/087b5c82addf90fd3a569364613e89b683f011a1/src/arraymancer/accessors_slicer.nim#L461
- https://github.com/mratsim/Arraymancer/blob/8551acb3561878c6effc04b5f39ee211e5f36031/src/arraymancer/operators_blas_l1.nim#L50
- https://github.com/mratsim/Arraymancer/blob/ab2bca5d772c054e71ac4ac1aaaa493655be149d/src/arraymancer/comparison.nim#L19
- https://github.com/mratsim/Arraymancer/blob/68a9c2bb4e7e84680446d5435ffb21f9896dcead/src/arraymancer/operators_extra.nim#L26