hll_out produces different results for the same value

``hll_out()`` doesn't unpack the value before outputting the ``bytea`` representation. That means that the same value could have two different output representations depending on how it is compressed internally.

Compression should only affect the internal representation, not the output. We should unpack it before outputting.

We should also consider a better output function that prints ``regwidth`` and ``log2m`` and omits irrelevant parts of the header.