Clash.Hedgehog.Sized.BitVector.genDefinedBitVector should not use genVec

[lmbollen]

Using genVec internally in genDefinedBitVector is incredibly slow and should be replaced. I think Hedgehog.Gen.intergral would significantly speed up generation..

[martijnbastiaan]

Be sure to test whether these generators generate numbers >= 2^63 for BitVector n where n => 64. It might rely on Enum internally which ~~is a severely broken class that in its current form should be banished from Haskell~~ can lead to surprising behavior.