REF: Make _slice_take_blocks_ax0 a generator
In some cases, the old `list[Block]` result was re-iterated over.
Do these actually improve perf? Or just for the principle of the thing? > Do these actually improve perf? Or just for the principle of the thing?

More principle and in theory save some list allocations (which don't really register in a speed improvement) Going to merge this PR, but happy to follow up if needed