Cardano Updates

* Make native_script fields era-prefixed as and when they are introduced
* Add smart constructors for script types in core
* Fix script_n_of_k for eras after allegra

Rename era-name-prefixed definitions with meaningful structural names
that are easier to reuse.

* Rename and move metadata, matadatum and metadatum_label definitions to
  core, along with transaction_index.
* Remove metadata_hash and just use
  auxiliary_data_hash everywhere.

in order not to lose the delegations that happened after the update,
before the end of the epoch

uniformly across eras

and add a test for it

and add a test for it

and add a test case for redelegating drep

for consistency

in order not to lose the delegations that happened after the update,
before the end of the epoch