Black - Python Code Formatter Contribution

Contributed a fix to Black, the uncompromising Python code formatter, resolving formatting issues with Python 3.12's new generics syntax. The fix ensures proper handling of type parameters when function parameters contain trailing commas.

Identified and fixed a bug in Black's formatting engine where functions with type parameters and trailing commas in their parameter lists were incorrectly formatted. The issue occurred in the `left_hand_split()` function, which processes both square brackets (for type parameters) and parentheses (for function parameters) as potential split points. When a trailing comma forced a split, the algorithm would incorrectly choose type parameter brackets instead of function parameter parentheses, causing malformed output. The solution involved modifying the split logic to avoid selecting parentheses as split points when they occur inside type parameter brackets, ensuring type parameters stay on the head line while the split correctly happens at the function parameter list. This contribution was merged into Black's main branch and is now used by millions of Python developers worldwide.