Use unsafe.string instead of unsafe.pointer

[karelbilek]

This only a cosmetic change, the speed seems to be exactly the same

Closes #371

[klauspost]

len() is not an operation. It is just a value read from register/memory, so you are not gaining anything.

I compared the assembly to the old code, and this always inserts a string length check. https://go.dev/src/runtime/unsafe.go - line 21 against int overflow. Since we have a valid byte slice we don't need this check, and will just add an extra branch to all use.

I suggest we abandon this change.

[karelbilek]

OK no problem