Fix Enum.min/2,3 and Enum.max/2,3 with a custom sorter on ranges

[pnezis]

The range clause of aggregate/3 only compared the two endpoints of the range, which is correct solely for sorters consistent with the natural integer order. Any other comparator returned a different result than the identical call on the equivalent list or stream:

sorter = fn a, b -> rem(a, 5) >= rem(b, 5) end
Enum.max(1..10, sorter)                         #=> 1, expected 4
Enum.max(Enum.to_list(1..10), sorter) #=> 4

Enum.min(-3..3, fn a, b -> abs(a) <= abs(b) end) #=> -3, expected 0

Only take the endpoint shortcut when the sorter is the default one (&>=/2 for max, &<=/2 for min); any custom sorter now reduces over the range elements like lists and streams do.

I am evaluating claude fable on code review tasks and this was one of the findings

[josevalim]

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