Improve Bitmap clear time and cleanup go ranges.

[romanalexander]

i := 0; i < len = 149.8 ns/op
clear() = 81 ns/op

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Note

Medium Risk
Mostly mechanical loop cleanups and a faster Clear, but bumping go.mod to Go 1.22 can break builds for consumers or CI pinned to older Go versions.

Overview
Speeds up fixed.Bitmap.Clear() by switching to the built-in clear() and modernizes several hot-path loops in boring and fixed bitmap/array operations to use Go 1.22’s for i := range n iteration.

Removes an unused min helper and updates go.mod to require Go 1.22 (enabling the new range syntax).

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