PERF: support mask in group_last

[jbrockmendel]

• closes #xxxx (Replace xxxx with the Github issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

xref #37493

We have existing tests with MaskedArrays for this.

[mroeschke]

Looks good. What's the perf diff for groupby.last?

Also the xref link doesn't seem to exist.

[jbrockmendel]

ser = pd.Series(range(10**5), dtype="Int64")
df = pd.DataFrame({"A": 1, "B": ser})
gb = df.groupby("A")

%timeit gb.last()
726 µs ± 26 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)  # <- main
527 µs ± 3.88 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)  # <- PR

Also the xref link doesn't seem to exist.

Fixed.

[mroeschke]

LGTM. Probably worth whatsnew in a followup as well.

[jreback]

sure assume first is an easy followup