Cardano Updates

Replace the manual segmented-witness serialization with MemoBytes,
which simplifies the code significantly. The block body is now
serialized as a flat 3-element list [invalid_transactions, transactions,
peras_certificate] instead of 5 separate segments.

Also fix PerasCert to encode/decode as bytes (matching CDDL),
reimplement alignedValidFlags using IntSet, and expose
DijkstraBlockBodyRaw/MkDijkstraBlockBody from Internal module.

Co-authored-by: Alexey Kuleshevich <[email protected]>

Change genArrayTerm from Gen to MonadGen so it can be used in
CBORGen contexts (e.g. custom CBOR generators for Huddle specs).

Co-authored-by: Alexey Kuleshevich <[email protected]>

- Add `blockBodySize` as a method on `EraBlockBody` with a default
  implementation using `EncCBORGroup`, replacing the standalone
  `bBodySize` function
- Remove `EncCBORGroup (BlockBody era)` superclass constraint from
  `EraBlockBody` so that eras can provide their own `blockBodySize`
  without needing `EncCBORGroup`

Co-authored-by: Alexey Kuleshevich <[email protected]>

Add plain DecCBOR instances for DijkstraBlockBodyRaw and
DijkstraBlockBody (needed for decoder equivalence tests), and a
custom ToExpr instance for DijkstraBlockBody. Add block_body to
the CddlSpec test suite.

Co-authored-by: Alexey Kuleshevich <[email protected]>

Define HuddleRule instances for "block_body" and "peras_certificate"
in the Dijkstra era, with a custom CBOR generator for block_body
that generates valid transaction indices. Update the CDDL spec to
match the new block structure: block = [header, block_body].

Co-authored-by: Alexey Kuleshevich <[email protected]>

The `Test.Cardano.Ledger.Alonzo.Binary.Golden.spec` is already getting
called in the `Test.Cardano.Ledger.Alonzo.GoldenSpec` module.

Added in order to be able to apply some function on the `txAuxData`
field of a transaction even when the `txAuxData` field is set to
`SNothing`.

When `actions/download-artifact` find only a single artifact, it uses a
different directory layout, with the artifact in the top-level directory
instead of a subdirectory

Co-authored-by: Alexey Kuleshevich <[email protected]>