Fix offset of the string dictionary length stream

[vuule]

Fixes #8514

String dictionary length is RLE encoded and rle_data_size and non_rle_data_size take this into account. However, When computing chunk stream offsets, these streams were treated as non-RLE and non_rle_data_size was not added. This caused discrepancy between non-RLE stream sizes and available space, leading to overlap between chunk streams.

Applied the non_rle_data_size to the offset to correct the discrepancy and added a test that uses decimal columns to increase the size of non-RLE encoded data and enable the overflow.

[codereport]

lgtm

[codecov]

Codecov Report

Merging #8538 (6b5a6ea) into branch-21.06 (2e780d0) will decrease coverage by 0.38%.
The diff coverage is n/a.

❗ Current head 6b5a6ea differs from pull request most recent head 4d31f6a. Consider uploading reports for the commit 4d31f6a to get more accurate results

@@               Coverage Diff                @@
##           branch-21.06    #8538      +/-   ##
================================================
- Coverage         82.83%   82.44%   -0.39%     
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  Files               109      109              
  Lines             17896    17542     -354     
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- Hits              14824    14463     -361     
- Misses             3072     3079       +7     

Impacted Files	Coverage Δ
python/custreamz/custreamz/tests/conftest.py	71.42% <0.00%> (-7.15%)	⬇️
python/cudf/cudf/io/hdf.py	50.00% <0.00%> (-7.15%)	⬇️
python/custreamz/custreamz/tests/test_kafka.py	35.71% <0.00%> (-7.15%)	⬇️
python/cudf/cudf/core/abc.py	87.80% <0.00%> (-3.11%)	⬇️
python/cudf/cudf/comm/gpuarrow.py	76.71% <0.00%> (-3.05%)	⬇️
python/cudf/cudf/benchmarks/bench_cudf_io.py	27.65% <0.00%> (-2.96%)	⬇️
python/cudf/cudf/utils/cudautils.py	55.04% <0.00%> (-2.72%)	⬇️
...ython/custreamz/custreamz/tests/test_dataframes.py	97.58% <0.00%> (-2.42%)	⬇️
python/cudf/cudf/api/extensions/accessor.py	92.59% <0.00%> (-0.75%)	⬇️
python/dask_cudf/dask_cudf/accessors.py	88.23% <0.00%> (-0.66%)	⬇️
... and 41 more

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