Fix issue with .real/.imag with string dtypes

[Illviljan]

np.array("").dtype.type[...] doesn't work to create an array.

• Use np.asarray to create the fill value array instead.
• Fix assert_eq so it uses np.array_equal for strings.

Closes #608

References
https://numpy.org/doc/stable/reference/arrays.scalars.html#indexing

[codecov]

Codecov Report

Merging #609 (c0f3c7a) into master (44e434d) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #609   +/-   ##
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  Coverage   91.95%   91.95%           
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  Files          20       20           
  Lines        3330     3330           
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  Hits         3062     3062           
  Misses        268      268           

[Illviljan]

Ready for review! The pre-commit errors looks unrelated.

[hameerabbasi]

Thanks for the patch!