Create a conversion function from Praos to PraosBatchCompat types

[iquerejeta]

Some of the new BatchCompat VRF types are compatible with the existing Praos types. In this PR we create conversion functions, to allow for a smooth transition between the compatible types.

In particular, we need the following conversion functions:

• skToBatchCompat :: SignKeyVRF PraosVRF -> SignKeyVRF BC.PraosBatchCompatVRF
• vkToBatchCompat :: VerKeyVRF PraosVRF -> VerKeyVRF BC.PraosBatchCompatVRF
• outputToBatchCompat :: OutputVRF PraosVRF -> OutputVRF BC.PraosBatchCompatVRF

We must include tests to guarantee the compatibility of these converted types.