Modularize lazy segment tree

[IvanRenison]

resolves #227, resolves #216

I have separated the operations of lazy segment tree in to functions so now it should be easy to modify.
I tested a modified operation with CSES Range Updates and Sums: https://cses.fi/paste/7b5c0925b9926d5f640805/

[IvanRenison]

Is this pull request going to be accepted or closed?

[IvanRenison]

@simonlindholm

[simonlindholm]

Is this pull request going to be accepted or closed?

Sorry for failing to respond to this. I've been hesitant to generalize the lazy segtree is the past, because there's so many possible variations, e.g. the classical sum/min/max interacting with add-on-range+set-on-range, but also wanting to support complex ad hoc pushing conditions, and I've felt like any generalization risks making things abstract and hard to understand and modify. The lazy segtree is due for a rewrite though, e.g. due to its bad performance, and there's been multiple people asking for this... So maybe. Although, KACTL is kinda in low maintenance mode atm, with me no longer actively competing, so I reckon it will take a while before anything happens on this front.