Cardano Updates

The metadatum decoder now only enforces bytes/text size limits (0..64)
for decoder versions > 2, matching the previous SoftForks.validMetadata
behavior. Tests are added to roundTripShelleyCommonSpec so they run for
every era: accepting oversized values at version 2 (Shelley) and
rejecting them from version 3 (Allegra) onwards.

Changes made with the help of an LLM

Forecast t BabbageEra = BabbageForecast t BabbageEra

`validateOutsideForecast`, `validateOutputTooBigUTxO`

This is the first set of changes to deprecate GetLedgerView et. al. from
cardano-ledger-tpraos.[^1]

This makes everything more type-safe, clearly separating TPraos forecasts
from those for Praos. It also distinguishes current from future forecasts
at the type-level.

[^1]: https://github.com/IntersectMBO/cardano-ledger/issues/5617

Since `ContextError`s are never stored and their reporting doesn't need
to be efficient (we always optimize for the positive case with valid
transactions, as invalid transactions don't propagate through the
network), there's no need for strictness annotations on the error
constructors.

This change removes the bang patterns (!) from:
- AlonzoContextError
- BabbageContextError
- ConwayContextError
- DijkstraContextError

Test that bytes/text up to 64 bytes decode successfully, and that
values exceeding 64 bytes are rejected.

Changes made with the help of an LLM

The decoder now enforces bytes/text size limits (0..64) for metadatums,
making the rule-level validMetadatum check redundant. Remove
validMetadatum, the SoftForks.validMetadata gate, and the Allegra
InvalidMetadata imp test that relied on constructing invalid metadatums
in-memory.

Changes made with the help of an LLM

*EraBlockHeader typeclasses deprecating BHeaderView

Enable Shelley anti-tests for update, proposed_protocol_parameter_updates,
protocol_param_update, and certificate. Enable Dijkstra transaction
arbitrary validate test that previously hung. Remaining xdescribes are
for unrelated issues.

Changes made with the help of an LLM

The CDDL spec requires `bytes .size (0..64)` and `text .size (0..64)`
for transaction metadatum, but the decoder did not enforce these limits.
This moves the size validation into `decodeMetadatum` so it aligns with
the CDDL spec. The `Arbitrary Metadatum` instance is also constrained
to produce valid values, and the previously disabled CDDL anti-tests
are now enabled.

Changes made with the help of an LLM

This also requires setting the decentralisation parameter `ppD` to `< 1`
so pools can produce blocks as well. We set it to `minBound` which means
that the network is full decentralised.