Reduce code duplication in horizontal and vertical filter functions

[sunsided]

Following up on #608, I took the liberty of reducing some code duplication in the horizontal_filter and vertical_filter functions.

Do note that this branches off #608 itself and therefore looks bigger than it actually is. The actual change is the introduction of the clamp_and_reset function. This comparison gives a better idea.

[theotherphil]

This looks good to merge after it’s been rebased.

[sunsided]

@theotherphil Done. 🫡

[theotherphil]

Thanks!