describe() fixes

[Jolanrensen]

Fixes #558 : Describe breaks on Number column

I'll first fix some of the most annoying bugs which can be found with describe(), more changes or fixes will come later.

Fixed:

• created col.isInterComparable() instead of col.isComparable() to avoid confusion
• cumsum:
  • added Short, Byte, BigInteger, Nothing support
  • (Short/Byte are supposed to become Int, similar to sum(), but they are temporarily converted back to Short/Byte so that the DataColumn.cumSum function returns the right type)
  • added extra tests
• mean:
  • added BigInteger support
  • added TODOs for BigDecimal and BigInteger, they're supposed to result in BigDecimal, not Double
• median:
  • added Float, Short, BigInteger support
  • Number support is still missing as it's not Comparable, will be handled later
  • added TODOs for conversion, will happen later
• min/max:
  • removed unused internal code
  • Number support is still missing as it's not Comparable, will be handled later
• std:
  • added BigInteger, Number support
  • added test for Byte
  • BigDecimal and BigInteger are supposed to result in BigDecimal, not Double, will be handled later
• sum:
  • added Float, Short, Byte, BigInteger, Number, Nothing support
  • added some tests
  • conversions will be handled later
• describe:
  • fixed @DataSchema type being String instead of KType
  • some cleaning up in the implementation
  • min, median, and max now also show up for Number columns with different types :) Numbers will be converted to double or BigDecimal first so they can be compared.

[koperagen]

Could you please add a test for #352? Maybe even if something else covers it, good to have one that is closer to use case

[koperagen]

isInterComparable is a new / not widespread term, for me it raises some questions like what's the difference (if i were to see it for the first time)
For users isComparable can be described as "filter columns for which max(), min(), median() and other (we actually only have 3) order operations make sense"
You wouldn't expect to find max() value for mixed column of String and Double values, so it should make things clearer

[Jolanrensen]

Well, that's actually the reason I changed it, because for me isComparable can be interpreted in two ways:

• "is comparable": so can call max(), min(), etc., not true for mixed number columns
• "is Comparable"; implements the interface, which would be true for mixed number columns

you need KDocs to explain what it actually means (and past-me didn't do a good job at that either). inter-comparable means "comparable inside" (or something, I came up with it too), which narrows down the meaning to the first. Of course, other name suggestions are very welcome if you can think of any :)

[Jolanrensen]

With suggestion of ChatGPT I'll rename it to .valuesAreComparable(). Would that be okay?

[Jolanrensen]

Could you please add a test for #352? Maybe even if something else covers it, good to have one that is closer to use case

Very good comment. After I added a test I noticed this PR didn't actually fully fix #352. It just fixed the error message. The actual issue needs to be solved separately. I will reorganize things a bit