Reduce allocations in remaining ecosystem comparators

[andrew]

PR #30 removes temporary allocations from SemVer, RubyGems, and NuGet comparison. The same scanner and stack-buffer approach should help the remaining scheme-specific comparators.

Measured at b8f1741 with Go 1.26.5 on darwin/arm64 using representative version pairs; current numbers re-measured at f59fa59:

• PyPI: replace PEP 440 regexp captures and release/local splits, currently about 1.13 µs, 802 B, and 6 allocs/op
• Maven: scan separators and digit/letter transitions without builders and temporary slices; Reduce Maven version component allocations #49 reduced this to about 531 ns, 720 B, and 15 allocs/op
• ALPM: done in Remove allocations from ALPM, Conan and Gentoo comparators #42, 0 allocs
• Conan: done in Remove allocations from ALPM, Conan and Gentoo comparators #42, 0 allocs
• Gentoo: done in Remove allocations from ALPM, Conan and Gentoo comparators #42, 0 allocs
• APK: compareAPK from Compare APK versions with apk-tools tokenization #45 builds a []apkToken per side (apk.go:41-42), currently 384 B and 2 allocs/op; apply the lockstep-iterator treatment and add it to TestEcosystemComparatorsDoNotAllocate
• OpenSSL: replace SplitN core parsing with direct indexes, currently about 102 ns, 96 B, and 2 allocs/op
• IntDot: compare dot-separated numeric components without temporary slices, currently about 105 ns, 112 B, and 2 allocs/op

Each change should keep exported APIs and scheme ordering unchanged, add differential or parity coverage against current behavior, and include before/after -benchmem results. PyPI and Maven should use separate focused PRs because their ordering rules are more involved.