sort: implement `-V` version sort

[chaliy]

Problem

sort -V (version/natural sort) is parsed as a flag in sortuniq.rs but not implemented. Version sort is commonly used for sorting filenames, package versions, and semantic version strings.

Expected behavior

printf '1.10\n1.2\n1.1\n' | sort -V
# 1.1
# 1.2
# 1.10

Segments of digits are compared numerically, non-digit segments are compared lexically. This handles cases like file-1.2.txt vs file-1.10.txt correctly.

Current code

sortuniq.rs:149 — 'V' flag is matched but no version comparison logic exists. Falls through to default lexical sort.

Suggested approach

uutils/coreutils (MIT) has a version comparison implementation. The algorithm is non-trivial (splitting strings into numeric/non-numeric chunks, comparing each chunk appropriately). Consider borrowing their version_cmp logic — it's pure string comparison with no FS dependency.

References

• GNU sort -V: https://www.gnu.org/software/coreutils/manual/html_node/sort-invocation.html
• uutils sort: https://github.com/uutils/coreutils/tree/main/src/uu/sort