fix: defer Quantity __array_ufunc__ for duck types - swev-id: astropy__astropy-13977

[casey-brooks]

Summary

• add a guard in Quantity.__array_ufunc__ to return NotImplemented when mixed operands include non-Quantity ducks exposing .unit while skipping table columns
• convert mixed-duck converter failures into UnitTypeError and reuse duck deferral helper logic
• extend duck interoperability tests to cover reflected operations and column interactions

Testing

• .venv310/bin/pytest astropy/units -q

Closes #69

[casey-brooks]

Test & Lint Summary

• .venv310/bin/pytest astropy/units -q
  • 2946 passed, 42 skipped, 5 xfailed

[rowan-stein]

Requesting review.

Summary:

• Change in astropy/units/quantity.py: Quantity.array_ufunc now returns NotImplemented early when inputs include an incompatible duck type (object exposes .unit but is neither Quantity nor ndarray), allowing reflected array_ufunc to proceed.
• Optional guarded converter handling to return NotImplemented for the same duck case on conversion failures, preserving existing behavior otherwise.
• Tests added to ensure reflected duck operations work and astropy.table.Column interactions remain unchanged.

Focus:

• Verify early guard correctness and that Column (ndarray subclass) behavior is unchanged.
• Ensure fast path performance is not impacted.
• Review tests for adequate coverage across add/mul/comparisons.

Closes #69.

[noa-lucent]

• Verified the new mixed-duck guard defers to foreign array_ufunc implementations without interfering with Quantity/Column or numpy inputs.
• Checked converter fallback paths and error translation; behavior for incompatible Quantity pairs remains unchanged and ducks now cleanly get control.
• Exercised the expanded test suite; coverage hits reflected dispatch, converter failures, numpy scalars/arrays, and Column interactions, and the docs summarize the new protocol.