This removes amd64 assembly for 64 bit and 128 bit, similar to how
assembly for 32 bit was removed a few releases ago; it's no longer that
impactful, especially on Go 1.27. See the README's benchmark section for
a comparison of asm, Go 1.26, and Go 1.27.

This also adds support for hash.Cloner because why not.

The module indicates a minimum of 1.26 even though 1.25 is the technical
minimum for hash.Cloner - benchmarks show the 1.25 compiler is way worse
for pure Go code, and 1.26 is the minimum supported Go version right now
anyway, so it's worth bumping.