Fix read_orc for decimal type

[rgsl888prabhu]

The run_pos which was being used was from data rather from secondary stream which was for scale, but resulted value was being used for secondary stream scale. The code change fixes that issue and also adds test case to cover the issue.

closes #7016

[vuule]

Good find 👍

[codecov]

Codecov Report

Merging #7034 (9c1f7df) into branch-0.18 (8c1f01e) will increase coverage by 0.19%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           branch-0.18    #7034      +/-   ##
===============================================
+ Coverage        82.03%   82.23%   +0.19%     
===============================================
  Files               96       96              
  Lines            16381    16670     +289     
===============================================
+ Hits             13438    13708     +270     
- Misses            2943     2962      +19     

Impacted Files	Coverage Δ
python/cudf/cudf/core/column/timedelta.py	89.16% <0.00%> (-0.38%)	⬇️
python/cudf/cudf/core/column/numerical.py	94.41% <0.00%> (-0.16%)	⬇️
python/cudf/cudf/core/column/string.py	86.48% <0.00%> (-0.10%)	⬇️
python/cudf/cudf/core/series.py	91.10% <0.00%> (ø)
python/cudf/cudf/_fuzz_testing/fuzzer.py	0.00% <0.00%> (ø)
python/cudf/cudf/core/column/datetime.py	89.42% <0.00%> (ø)
python/cudf/cudf/utils/hash_vocab_utils.py	100.00% <0.00%> (ø)
python/dask_cudf/dask_cudf/io/tests/test_csv.py	100.00% <0.00%> (ø)
python/cudf/cudf/core/column/categorical.py	93.35% <0.00%> (+0.01%)	⬆️
python/cudf/cudf/core/column/column.py	88.14% <0.00%> (+0.10%)	⬆️
... and 6 more

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