Pass generate_decimal256_case integration test, add DataType::Decimal256

[viirya]

Which issue does this PR close?

Closes #2093.

Rationale for this change

What changes are included in this PR?

Are there any user-facing changes?

[codecov-commenter]

Codecov Report

Merging #2094 (9b005d3) into master (efd3152) will decrease coverage by 0.04%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master    #2094      +/-   ##
==========================================
- Coverage   83.73%   83.68%   -0.05%     
==========================================
  Files         225      225              
  Lines       59412    59461      +49     
==========================================
+ Hits        49748    49760      +12     
- Misses       9664     9701      +37     

Impacted Files	Coverage Δ
arrow/src/array/equal/decimal.rs	96.29% <0.00%> (-3.71%)	⬇️
arrow/src/array/transform/fixed_binary.rs	68.18% <0.00%> (-6.82%)	⬇️
arrow/src/datatypes/field.rs	54.45% <0.00%> (-0.14%)	⬇️
arrow/src/ipc/reader.rs	90.82% <ø> (ø)
integration-testing/src/lib.rs	0.00% <0.00%> (ø)
parquet/src/arrow/arrow_writer/mod.rs	97.53% <ø> (ø)
arrow/src/ipc/convert.rs	93.71% <23.07%> (-1.87%)	⬇️
arrow/src/array/data.rs	84.88% <33.33%> (-0.07%)	⬇️
arrow/src/datatypes/datatype.rs	62.88% <33.33%> (-1.53%)	⬇️
arrow/src/array/equal/mod.rs	96.34% <50.00%> (-0.14%)	⬇️
... and 8 more

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[alamb]

This is very cool @viirya

I wonder if anyone else has thoughts about how to name the new DataType?

[alamb]

Should we also rename Decimal to Decimal128?

Or maybe use an extra mode in Decimal like `

enum BitWidth {
  // 128 bits
  Bits128,
  // 256 bits
  Bits256,
}


enum DataType {
..
  Decimal(usize, usize, DecimalWidth)
}

[viirya]

I thought to add a parameter to current Decimal like you put above. But soon I realize that I need to modify many places. And we need to do bit width check there. As in C++ and Python implementations, they have Decimal128Type and Decimal256Type separately. I feel that it is simple to work with.

And, yea, we need to rename Decimal to Decimal128. Although I've not done it in this change as this is basically for Decimal256 interop test. I may work on it in another PR.

[alamb]

And, yea, we need to rename Decimal to Decimal128.

I agree

I may work on it in another PR.

Thank you!

[alamb]

I see #2101 as well so 👍

[ursabot]

Benchmark runs are scheduled for baseline = 576069a and contender = fd38664. fd38664 is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ursa-thinkcentre-m75q] ursa-thinkcentre-m75q
Buildkite builds:
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java