feat: add Needleman-Wunsch global sequence alignment algorithm

[Sanchana05]

Description: Added the Needleman-Wunsch algorithm for optimal global sequence alignment to Dynamic programming

Changes:

1. Implemented needleman_wunsch DP matrix filling and traceback.

2. Added comprehensive docstrings, including matching/mismatch/gap penalty logic.

3. Included passing doctests for validation.

4. Strictly adhered to pure Python (no external dependencies).

5. Added type hinting for all functions.

[algorithms-keeper]

Closing this pull request as invalid

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