Closes #5252: alignment tests for arkouda.numpy.dtypes

[ajpotts]

Add NumPy alignment tests for dtypes and unary ufuncs

Summary

This PR introduces a new NumPy-alignment verification test suite for Arkouda dtypes and selected unary ufuncs. The goal is to explicitly codify current behavior, surface gaps vs NumPy semantics, and provide a structured place to track alignment progress over time.

What’s Included

• New test file: tests/numpy/alignment_verification/dtypes_alignment.py
• Adds coverage for:
  • ak.dtype (string specs, Python scalars, bigint threshold)
  • resolve_scalar_dtype
  • can_cast (including NumPy parity checks)
  • result_type (including bigint vs float precedence)
  • get_byteorder
  • Unary ufunc alignment scaffold (absolute, negative, floor, ceil)
• Registers the new test file in pytest.ini

Notable Design Decisions

• Bigint handling: ak.result_type is asserted to return dtype("bigint"), matching NumPy’s result_type contract of returning a dtype, not a Python type.
• Unary ufunc gaps:
  • ak.floor / ak.ceil are marked as xfail for integer inputs.
  • NumPy supports integer inputs for these ufuncs; Arkouda currently restricts them to floats.
  • A follow-up issue tracks this gap explicitly.

Related Issue

• Support integer inputs for ak.floor / ak.ceil (NumPy alignment)

Why This Matters

• Makes Arkouda’s current dtype semantics explicit and testable
• Prevents silent regressions in dtype promotion and casting logic
• Provides a clear, incremental path toward tighter NumPy compatibility

Testing

pytest tests/numpy/alignment_verification/dtypes_alignment.py

All existing tests continue to pass; new failures are limited to intentional xfails that document known gaps.

Closes #5252: alignment tests for arkouda.numpy.dtypes