vim-patch:9.2.0937: sort() with a numeric option converts each item on every comparison (#41286)

Problem:  sort() with "n", "N" or "f" converts an item to its number on
          every comparison.  For "n" that is a tv2string() plus strtod()
          per comparison, so sorting a list of numbers turns each number
          into a string and back O(n log n) times, dwarfing the sort.
Solution: Compute the numeric key of each item once, before the sort,
          and compare the stored key (Samuel Schlesinger).  Only the
          builtin numeric compare modes are affected; uniq(), which
          passes a bare list item to the compare function, and the
          string and user-function paths are unchanged.

Sorting a list of 100000 numbers (min of 3, macOS arm64):
- sort(l, 'n'):  0.205s -> 0.017s
- sort(l, 'N'):  0.017s -> 0.010s
- sort(l, 'f'):  0.014s -> 0.010s
The result is identical, including that a string is still treated as 0
in "n" mode and that "N" keeps full 64-bit precision.

Add Test_sort_numeric_precomputed(): a large shuffled list sorted with
"n", mixed integers and floats, int64 values beyond the exact range of
a double for "N", and uniq() over the non-precomputed path.

closes: vim/vim#21003

https://github.com/vim/vim/commit/c8c59db9dfdc2db5f17aa0a78ea1464f035bdf5e

Co-authored-by: Samuel Schlesinger <sgschlesinger@gmail.com>
Co-authored-by: Claude <noreply@anthropic.com>

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