Add BigDecimal instances for cats

[FunFunFine]

This MR add missing Semigroup and Monoid instances for Pos/NegBigDecimal.

[codecov[bot]]

Codecov Report

Merging #1088 (0fb7166) into master (636e505) will decrease coverage by 0.04%. The diff coverage is 100.00%.

:exclamation: Current head 0fb7166 differs from pull request most recent head b0eac29. Consider uploading reports for the commit b0eac29 to get more accurate results

@@            Coverage Diff             @@
##           master    #1088      +/-   ##
==========================================
- Coverage   92.64%   92.61%   -0.04%     
==========================================
  Files          63       63              
  Lines         829      839      +10     
  Branches       26        8      -18     
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+ Hits          768      777       +9     
- Misses         61       62       +1     

Impacted Files	Coverage Δ
...c/main/scala/eu/timepit/refined/cats/package.scala	94.11% <100.00%> (+0.27%)	:arrow_up:
...rc/main/scala/eu/timepit/refined/util/string.scala	0.00% <0.00%> (ø)
...main/scala/eu/timepit/refined/scodec/package.scala	100.00% <0.00%> (ø)
...n/scala/eu/timepit/refined/predicates/string.scala	100.00% <0.00%> (ø)
...n/scala/eu/timepit/refined/scalaz/derivation.scala	100.00% <0.00%> (ø)
...u/timepit/refined/shapeless/typeable/package.scala	100.00% <0.00%> (ø)
...rc/main/scala-3.0-/eu/timepit/refined/string.scala	98.79% <0.00%> (+0.02%)	:arrow_up:

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[FunFunFine]

Hi @fthomas , can you merge this MR please?

[fthomas]

@FunFunFine Could you add tests for these instances to https://github.com/fthomas/refined/blob/master/modules/cats/shared/src/test/scala/eu/timepit/refined/cats/CommutativeSemigroupAndMonoidLawTests.scala ?

[FunFunFine]

@fthomas it's been a while, but here it goes.

[fthomas]

Thanks @FunFunFine!

Can we also add commutativeSemigroup / commutativeMonoid tests like this:

checkAll("CommutativeSemigroup[PosBigDecimal]", CommutativeSemigroupTests[PosBigDecimal].commutativeSemigroup)

Or do they also fail because those instances are only approximately associative, too (like PosDouble for example)?

[FunFunFine]

The compilation fails with the following error when I try to add this test:

diverging implicit expansion for type org.scalacheck.Arbitrary[(scala.math.BigDecimal, eu.timepit.refined.numeric.Greater[shapeless._0])]
starting with method arbTuple2 in trait ArbitraryArities
  checkAll("CommutativeSemigroup[PosBigDecimal]", CommutativeSemigroupTests[PosBigDecimal].commutativeSemigroup)

I don't really understand what the problem is because it works for other types, but not for BigDecimal apparently.

[fthomas]

Oh, that fails because we lack Arbitrary instances for refined BigDecimal types. I'm fine with merging this without these tests then.

[FunFunFine]

Someone who has access to merging needs to merge it