LeetCode 1143: Longest Common Subsequence

## [LeetCode 1143: Longest Common Subsequence](https://leetcode.com/problems/longest-common-subsequence/)

**Difficulty:** Medium
**Category:** DP - Multidimensional

### Tasks
- [ ] Implement solution in `src/dp_multidimensional/longest_common_subsequence.py`
- [ ] Verify tests pass: `pytest tests/test_longest_common_subsequence.py`
- [ ] Analyze time and space complexity