Add sum functions

[planetis-m]

Alternative to #16004, addresses most review comments. If it's going to be deprecated, I can adopt the package, either works for me. I am the original author.

[konsumlamm]

While I like the idea of having different accurate summation functions, I don't think they should be in the standard library (and I'm not sure why this module was added in the first place), but rather a nimble package.

The only real use of std/sums I could find (after a quick GitHub search) was in a test, where it only seems to be used to test passing as openArray (https://github.com/bpr/vla/blob/master/tests/tests.nim). So, similar to #18395 (comment), I'm in favor deprecating std/sums, as it's only very rarely used (definitely not enough to justify having it in the standard library).

[planetis-m]

Alright, will do that instead.