Closes #5272: alignment tests for arkouda.numpy.pdarraysetops

[ajpotts]

Add NumPy alignment test suite for pdarray set operations

Summary

This PR adds a comprehensive NumPy-alignment test suite for Arkouda pdarray set operations, covering:

• in1d
• union1d
• intersect1d
• setdiff1d
• setxor1d
• concatenate
• indexof1d
• multi-array (row-wise) set operations

The goal is to explicitly verify semantic alignment with NumPy behavior and to surface existing deviations in a controlled, well-documented way.

What’s included

• New test file:
  • tests/numpy/alignment_verification/pdarraysetops_alignment.py
• Test coverage added to pytest.ini so the suite runs as part of standard alignment verification.
• Careful handling of assume_unique=True cases:
  • Inputs are explicitly uniqued before calling Arkouda, matching NumPy’s contract.
• Multi-array set operations validated using NumPy structured arrays as a reference model.

Known issues (documented via xfail)

• ak.union1d does not match NumPy semantics when one input is empty.
  • Arkouda returns the non-empty input unchanged (preserving duplicates and order).
  • NumPy returns sorted unique values.
• These cases are marked with xfail and linked to Issue Bug: ak.union1d not NumPy-aligned for empty-input cases (returns non-unique / unsorted) #5273, so the suite remains informative but non-blocking.

Why this matters

• Establishes a clear, executable contract between Arkouda and NumPy for set operations.
• Prevents regressions as internal implementations evolve.
• Separates test correctness issues (e.g., misuse of assume_unique) from real semantic gaps in Arkouda.

Follow-up work

• Fix ak.union1d empty-input fast paths to apply unique + sort.
• Remove corresponding xfails once behavior matches NumPy.

Testing

• All existing tests pass.
• New alignment suite passes with expected xfails.

Closes #5272: alignment tests for arkouda.numpy.pdarraysetops

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[1RyanK]

I'm not too worried about the comments but I figure it could be a while before someone comes back to this test and this might make things simpler...?