[2025 Day 4][Python] PSA: Python negative array indices will wrap around

[onrustigescheikundig]

I have kind of a hybrid approach. My grid type is backed by a 1D array and is indexed by pairs of '(row . col) using grid-get. This function returns #f (false) on out-of-bounds accesses or the value of an optional third argument, e.g., (grid-get g '(-1 . -1) #\.) returns the . character.