A city has a few air-quality stations. Each one records a pollution reading every day. The readings come as a grid: one row per day and one column per station.
A reading is over the limit when it is strictly greater than limit.
Task: write over_limit(readings, limit) and return a dict:
"per_station" — for each station, in column order, how many days it was over the limit,"bad_days" — how many days had every station over the limit at once.The grid always has at least one day and one station.