Describe breaks on `Number` column (and other statistics inconsistencies)

[Jolanrensen]

This happens because the Iterable<Number>.std() function accepts Number but doesn't convert them to Double (like mean() does).

There are a couple more missing actually:

• cumSum
  • Misses Byte, Short
  • Has DataColumn overloads but not Iterable/Sequence
• mean
  • Has Sequence<Double | Float> but not for other Number types
• median
  • Misses Float, Byte, Short, Number (it only works on Comparable)
  • Needs to handle other types consistently
  • No Sequence overloads
  • Cannot skipNA (if applicable)
• min and max
  • internal Iterable<T>.min and max are not used and can be removed. Stdlib functions for Comparable sequences and iterables are used instead.
  • Misses Number (it only works on Comparable)
• std
  • Breaks if type is Number
  • Short and Byte are cast to Int which works but is a bit iffy
  • Iterable overloads missing for Number, Short, Byte
  • Sequence overloads missing
  • Nullable overloads missing for Iterable (and sequence)
• varianceAndMean
  • also provides std(ddof: Int) function without docs of what ddof even means, as well as count. Could have a better name. Also can produce nulls?? this screams for documentation.
  • variance functions are missing on DataColumns entirely (had to be added separately for Kandy)
  • Misses Short, Byte, Number, and nullable overloads
  • Misses Sequence overloads
• sum
  • Has TODOs where types are amiss
  • Misses Float(!), Short, Byte, Number in various Iterable overloads.

All are also missing BigInteger as we're supporting BigDecimal too.

[koperagen]

#352 probably same problem

[Jolanrensen]

As mentioned here #543, some functions like median(ints) might result in an unexpectedly rounded Int in return. It might be better to let all functions return Double and then handle BigInteger / BigDecimal separately for now, as they're java-specific for now.