Remove IO.blocking from array copy in S3 client.

[LeifW]

• Also remove the array copy - using .asByteArrayUnsafe instead of .asByteArray to return the original byte array without making a copy of it. FS2 doesn't mutate the byte array afaict, and this readFileMultipart method returns a fs2.Stream[F, Byte] - the caller isn't going to be able to mutate those Bytes.

• Also removed the Monad.ifM. ifM(pure(x))(t, f) is the same as if (x) t else f.

• Construct the Chunks from byte arrays in a more direct fashion.