Fix pivot_table duplicate indices with Python 3.14 + NumPy 1.26 #63324
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Summary
fixes #63314 - pivot_table creating duplicate indices on python 3.14 with numpy 1.26
tracked down the actual bug. wasn't in compress_group_index like i thought - it's numpy's searchsorted that's broken with this version combo.
What was happening
The fix
fallback to the np.unique approach when on python 3.14 + numpy < 2.0. this is the same method the non-sorted path already uses, so it's tested.
Testing
tested with the reproduction case from the issue (100k rows, 3 metrics). works correctly now.