REF: use concat_compat in union_with_duplicates

[jbrockmendel]

• closes #xxxx
• tests added / passed
• Ensure all linting tests pass, see here for how to run them
• whatsnew entry

[jreback]

wow

any perf implications?

[jbrockmendel]

any perf implications?

we're going to take a small hit bc isinstance(obj, ABCFoo) is slower than isinstance(obj, Foo), and the runtime import of ensure_wrapped_if_datetimelike (i guess could move that to dtypes.cast). the union cases we'll take a hit in non-EA cases bc concat_compat is slower than np.concatenate, but for EA cases we ought to do better

[jreback]

any perf implications?

we're going to take a small hit bc isinstance(obj, ABCFoo) is slower than isinstance(obj, Foo), and the runtime import of ensure_wrapped_if_datetimelike (i guess could move that to dtypes.cast). the union cases we'll take a hit in non-EA cases bc concat_compat is slower than np.concatenate, but for EA cases we ought to do better

sounds good about moving that, but this looks fine.