Closes #5242: alignment tests for arkouda.numpy.char

[ajpotts]

Add NumPy-alignment tests for arkouda.numpy.char.isnumeric

Summary

This PR introduces a new NumPy-alignment test suite for arkouda.numpy.char, with an initial focus on isnumeric.
The tests explicitly compare Arkouda behavior against Python and NumPy semantics and surface a known mismatch for empty strings.

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What’s Included

• New test module: tests/numpy/alignment_verification/char_alignment.py
• Registration of the new test module in pytest.ini
• Coverage for:
  • Public API re-exports (bool_, int_, str_, etc.)
  • Type validation errors
  • Exact result parity with np.char.isnumeric
  • Unicode numeric edge cases
  • Deterministic randomized testing against Python + NumPy

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Known Failure (Documented)

Two tests are marked xfail due to a known semantic mismatch:

"".isnumeric()          # Python / NumPy → False
Arkouda → True

This is a known issue where empty strings are treated as numeric due to a vacuous
"all characters are numeric" check.

Tracked separately (Issue #5243).

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Why This Matters

• Establishes a reusable pattern for NumPy-alignment verification
• Prevents silent divergence in string semantics
• Strengthens pandas / NumPy compatibility guarantees
• Makes current behavior differences explicit and test-documented

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Follow-up Work

• Fix Strings.isnumeric() to treat empty strings as non-numeric
• Remove xfail markers once behavior matches NumPy

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Diff Summary

• pytest.ini: include new alignment test module
• tests/numpy/alignment_verification/char_alignment.py: new tests

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Notes

• Unicode numeric literals are intentional; # noqa: RUF001 is used where appropriate
• Randomized test is deterministic and low-cost

Closes #5242: alignment tests for arkouda.numpy.char