Mostly it's about Go 1.22+ syntax with ranging over integers, but it also
prefers ranging over slices where possible (it makes code a little better to
read).
Notice that we have a number of dangerous loops where slices are mutated
during loop execution, many of these can't be converted since we need proper
length evalutation at every iteration.
Signed-off-by: Roman Khimov <roman@nspcc.ru>
NewMerkleTree is a memory hog, we can do better than that:
BenchmarkMerkle/NewMerkleTree-8 13 88434670 ns/op 20828207 B/op 300035 allocs/op
BenchmarkMerkle/CalcMerkleRoot-8 15 69264150 ns/op 0 B/op 0 allocs/op
buildMerkleTree() is internal to the hash package and if anyone calls it with
`len(leaves) == 0` he deserves a panic. As it's the only error case in it, we
can remove error value return from this function and simplify NewMerkleTree().
Go's Hash is explicitly specified to never return an error on Write(), and our
own decoding functions only check for length which is gonna be right in every
case so it makes no sense returning errors from these functions.
