Shortest Path in a Blocked Maze

Overview

Given a 2D grid maze with start ('S'), end ('E'), open cells ('.'), walls ('#'), and obstacles ('X'), find the shortest path from S to E using up/down/left/right movement.

Rules

• Movement is restricted to up, down, left, and right
• '#' and 'X' cells are impassable
• Return None if no path exists
• Return a list of (row, col) coordinates from S to E inclusive
• Raise ValueError for invalid input (empty, ragged rows, missing/duplicate S or E, invalid characters)

Scoring

Gradient scoring based on test cases passed (12 tests total).