[Requires Arrow spec] Added support for decimal 32 and 64

[jorgecarleitao]

This is being worked over the arrow mailing list and apache/arrow#8578 . It is marked as draft until it is officially supported / abandoned if abandoned by the official implementation.

Note that this PR is backward incompatible: DataType::Decimal(usize,usize) needs a new argument to differentiate between different physical types backing the (logical) decimal type.

Before:

use arrow2::datatypes::DataType;

let precision = 5;
let scale = 5;
let data_type = DataType::Decimal(precision, scale);

After:

use arrow2::datatypes::{DataType, DecimalType};

let precision = 5;
let scale = 5;
let data_type = DataType::Decimal(DecimalType::Int128, precision, scale);

where DecimalType is an enum with 3 different variants (Int32, Int64, Int128).

Because the other variants have an existing physical representation (i32 and i64 respectively), most of this crate works out of the box (growable, filter, take, comparison (including simd), etc.). There is still some work for the aggregations (decimal is not yet supported), cast, and arithmetics (arithmetics for decimals work a bit different due to the precision/scale constraints).

We also need to think about how to support reading from and writing to parquet (i.e. we may be able to read a parquet decimal i32 to a decimal i32 instead of i128 as we do it now).

[codecov]

Codecov Report

Merging #896 (cfb7ff5) into main (735218b) will decrease coverage by 13.43%.
The diff coverage is 65.34%.

❗ Current head cfb7ff5 differs from pull request most recent head fd66c1f. Consider uploading reports for the commit fd66c1f to get more accurate results

@@             Coverage Diff             @@
##             main     #896       +/-   ##
===========================================
- Coverage   83.67%   70.24%   -13.44%     
===========================================
  Files         365      347       -18     
  Lines       35865    18925    -16940     
===========================================
- Hits        30009    13293    -16716     
+ Misses       5856     5632      -224     

Impacted Files	Coverage Δ
src/compute/aggregate/min_max.rs	65.16% <0.00%> (-15.39%)	⬇️
src/compute/arithmetics/decimal/mod.rs	100.00% <ø> (+1.33%)	⬆️
src/compute/arithmetics/mod.rs	69.81% <ø> (-4.30%)	⬇️
src/compute/comparison/mod.rs	55.78% <ø> (+1.04%)	⬆️
src/compute/take/mod.rs	65.85% <ø> (-23.04%)	⬇️
src/io/avro/write/schema.rs	64.86% <0.00%> (-12.22%)	⬇️
src/io/json_integration/write/schema.rs	0.00% <0.00%> (ø)
src/io/odbc/read/schema.rs	0.00% <ø> (ø)
src/io/parquet/read/schema/convert.rs	74.34% <0.00%> (-19.88%)	⬇️
src/types/mod.rs	0.00% <0.00%> (-100.00%)	⬇️
... and 395 more

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