(fix) apply formatting fixes for pre-commit compliance

[mark14wu]

(fix) apply formatting fixes for pre-commit compliance

Apply black, isort, trailing whitespace, end-of-file fixes.
Fix flake8 errors: E731, F841, F401, E501.

PR chain

1. 👉 (fix) apply formatting fixes for pre-commit compliance #17 👈 YOU ARE HERE
2. (add) pre-commit linter CI workflow #18

Summary

Apply formatting and linting fixes to bring the codebase into compliance with pre-commit hooks (black, isort, flake8, trailing whitespace, end-of-file).

Flake8 error codes fixed

• E731: Do not assign a lambda expression; use a def instead. e.g. grid = lambda meta: (...) → def grid(meta): return (...)
• F841: Local variable is assigned but never used (dead code).
• F401: Module imported but unused. e.g. import torch with no reference to torch in the file.
• E501: Line too long (exceeds 88 characters).

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