Add support for null and non-numeric types in Series.diff and DataFrame.diff

[Matt711]

This PR supports non-numeric data types (timestamp and ranges) in Series.diff and DataFrame.diff. In DataFrame.diff, datetime ranges are already supported because DataFrame.shift works. But Series.diff doesn't use the Series.shift implementation, so there wasn't support for datetime ranges.

import datetime
dti = pd.to_datetime(
    ["1/1/2018", np.datetime64("2018-01-01"), datetime.datetime(2018, 1, 1), datetime.datetime(2020, 1, 1)]
)
df = DataFrame({"dates": dti})
df.diff(periods=periods, axis=axis)

closes #10212.

[GPUtester]

Can one of the admins verify this patch?

[bdice]

add to allowlist (edit: looks like this didn't work. I may not have privileges to add Matt to the list of allowed CI users.)

[sevagh]

add to allowlist

[codecov]

Codecov Report

Merging #10625 (eef9434) into branch-22.06 (8f5a044) will increase coverage by 0.06%.
The diff coverage is 57.14%.

❗ Current head eef9434 differs from pull request most recent head 3229a3a. Consider uploading reports for the commit 3229a3a to get more accurate results

@@               Coverage Diff                @@
##           branch-22.06   #10625      +/-   ##
================================================
+ Coverage         86.34%   86.41%   +0.06%     
================================================
  Files               142      142              
  Lines             22356    22334      -22     
================================================
- Hits              19304    19299       -5     
+ Misses             3052     3035      -17     

Impacted Files	Coverage Δ
python/cudf/cudf/core/dataframe.py	93.75% <ø> (-0.01%)	⬇️
python/cudf/cudf/utils/cudautils.py	65.74% <ø> (+5.90%)	⬆️
python/cudf/cudf/core/series.py	95.15% <57.14%> (-0.13%)	⬇️
python/cudf/cudf/core/column/numerical.py	95.88% <0.00%> (-0.30%)	⬇️
python/cudf/cudf/core/groupby/groupby.py	91.72% <0.00%> (+0.22%)	⬆️
python/cudf/cudf/core/column/string.py	89.22% <0.00%> (+0.24%)	⬆️
python/cudf/cudf/core/tools/datetimes.py	84.49% <0.00%> (+0.30%)	⬆️
python/cudf/cudf/core/column/lists.py	92.79% <0.00%> (+1.27%)	⬆️

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[beckernick]

By ripping out the diff numba kernel and using shift + binary op, I believe this will provide null support. Perhaps worth reflecting including in the PR title for the changelog?

[Matt711]

@gpucibot merge

[bdice]

@gpucibot merge