Search Words in a Character Grid

You are given a 2D grid of lowercase English letters. Part 1: Given a single target word, determine whether the word can be formed by a path in the grid. A path may start from any cell, and each next character must be in a horizontally or vertically adjacent cell. The same grid cell cannot be used more than once in the same path. Part 2: As a follow-up, you are given a list of target words. Return all words from the list that can be formed in the grid under the same adjacency and no-reuse rules. Design the solution to be efficient when the word list is large and many words share prefixes. Implement the required function or functions, describe the expected time and space complexity, and handle edge cases such as empty grids, empty word lists, duplicate words, and words longer than the number of cells.