ColBytes support for LowCardinality

i'm trying to avoid converting `[]byte` types into `string` for bulk inserts w/ low-cardinality cols but the API doesn't seem to allow that since `[]byte` is not `comparable`

as a workaround, I can use ColString and then coerce the `[]byte` vals into `string` with the unfortunate side-effect of additional allocations. ideally this would not be needed and the API would support low-cardinality w/ `[]byte` natively.