Lantern Maze

Task

Lantern Maze is a small grid game. A level is a map of walls, floor, a start, an exit and lanterns. The rules engine has checks that fail, a path finder that was never written, and a lighting count that is too slow for large maps. Work through it in three stages: make the failing checks pass, write the path finder, then make the lighting count fast.

Requirements

1. play(lines, request) takes a map and one request, and returns a small object. A map is a nonempty list of nonempty strings of equal length (ValueError containing map otherwise). # is a wall; every other character is an open cell. The edge of the map is the edge of the world. Do not change the arguments.
2. Stage 1. {op: "size"} returns {rows, cols}. {op: "neighbors", cell: [row, col]} returns {neighbors}: the open cells one step up, down, left and right of the cell, in that order, each as [row, col]. A cell outside the map raises ValueError containing cell. Any other op raises ValueError containing op.
3. Stage 2. {op: "path"} returns {steps}: the fewest steps from S to E, moving one open cell at a time, or -1 when E cannot be reached. The map must have exactly one S and one E (ValueError containing map otherwise).
4. Stage 3. {op: "lit", radius} returns {lit}: how many open cells are within radius steps of at least one lantern (L), walking through open cells only, so walls block light. A lantern lights its own cell. radius is a non-negative integer (ValueError containing radius otherwise). The count must finish on a 150 by 150 map with thousands of lanterns.