use unsafeBytesToString to reuse memory

[yjhmelody]

I found that some operations are very expensive about mem alloc when string(bytes).
Such as:

So I try to reuse some mems by using unsafe.

[mitar]

Just for the record, this is done inside standard library as well: https://go.dev/src/strings/builder.go#L46

[mitar]

Although there will be soon official public API to do this: golang/go#53003