Fix octal pattern matching in regex string

[davidwendt]

Closes #9946

Fixes decoding logic in regex pattern compile step to consume only up to the last octal character. The original logic was incorrectly discarding the next pattern character. And if the octal characters were specified at the end of the pattern invalid bytes were read passed the end of the pattern. This is what caused the intermittent failure since sometimes the invalid bytes were 0 which masked the issue.

This PR also includes tests for octal patterns in various positions in the regex pattern.

[codecov]

Codecov Report

Merging #9993 (377ab9d) into branch-22.02 (967a333) will decrease coverage by 0.07%.
The diff coverage is n/a.

@@               Coverage Diff                @@
##           branch-22.02    #9993      +/-   ##
================================================
- Coverage         10.49%   10.41%   -0.08%     
================================================
  Files               119      119              
  Lines             20305    20498     +193     
================================================
+ Hits               2130     2134       +4     
- Misses            18175    18364     +189     

Impacted Files	Coverage Δ
python/custreamz/custreamz/kafka.py	29.16% <0.00%> (-0.63%)	⬇️
python/dask_cudf/dask_cudf/sorting.py	92.30% <0.00%> (-0.61%)	⬇️
python/cudf/cudf/__init__.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/frame.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/index.py	0.00% <0.00%> (ø)
python/cudf/cudf/io/parquet.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/series.py	0.00% <0.00%> (ø)
python/cudf/cudf/utils/utils.py	0.00% <0.00%> (ø)
python/cudf/cudf/utils/dtypes.py	0.00% <0.00%> (ø)
python/cudf/cudf/utils/ioutils.py	0.00% <0.00%> (ø)
... and 20 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 093b0ad...377ab9d. Read the comment docs.

[codereport]

lgtm 👍

[davidwendt]

@gpucibot merge