[Feature] Improve scheduling algorithm for loops

[markoshorro]

Description of the problem or scenario potentially improvable:

Currently all code is generated ad-hoc, there is no much logic on the greedy algorithm that packs together the operations. This is because we're assuming that we know all the sizes of the loops, but there could be cases where we don't.

Description of the solution

Create a pass/stage for analyzing the code size/latency/cycles ONLY of the loop.

Side effects or any other known issues caused by this feature:

Better scheduling for the loop. This could slow down a lot if there are many loops, so this shouldn't be a long/heavy stage. Aim for parallelism whenever possible.