Cardano Updates

Enumerates every remaining caller of the deprecated surface after
#5271: production (Cardano.Wallet.hs, Server.hs), old tx builder
(Shelley/Transaction.hs, partially overlaps with #5243), integration
tests (Shared/Transactions.hs, addRequiredSigners in TransactionsNew)
and unit tests (TransactionSpec, TransactionLedgerSpec).

Organises the work into three phases:
  A. reachable without #5243 (4 sites)
  B. unit-test migration (~20 sites, two files)
  C. delete the bridge functions and the three Cardano.Api*
     imports in SealedTx.hs

Introduce sealedTxFromLedgerTx :: Read.IsEra era => Read.Tx era -> SealedTx.
Serialises via Read.serializeTx (ledger-native) and wraps in EraValue
without any cardano-api involvement.

Migrate sealWriteTx in Transaction.Ledger.hs to use the new
constructor, pattern-matching on RecentEra to witness the era.
Removes the toCardanoApiTx -> sealedTxFromCardano' roundtrip,
dropping the Cardano.Api.Extra import from that module.

Step 2a of SealedTx decommission plan.

Following the migration of parsePartialTx to deserializeTx,
cardanoTxInExactEra has no external callers. Remove it along
with the now-redundant Data.Data import in SealedTx.hs.

Replace cardanoTxInExactEra (cardano-api path) with
deserializeTx (ledger-native) in the redeemer-bearing
partial tx parser. Pattern-matches on RecentEra era so
the era singleton witnesses the target ledger type.

One fewer caller of cardano-api's
'deserialiseFromCBOR / InAnyCardanoEra Cardano.Tx' path.
'fromCardanoApiTx' → direct use of 'Read.Tx era' unwrapped
into 'Write.Tx era'.

Replace the cardano-api path
(SealedTx → unsealShelleyTx → TxInMode → toConsensusGenTx → GenTx)
with a direct ledger-native path
(SealedTx → unsafeReadTx :: EraValue Read.Tx → consensusGenTxFromTxRecent → GenTx).

The stored 'EraValue Read.Tx' already knows its era, so the
separate 'readCurrentEra' query is no longer needed, and
'TxInMode' / 'toConsensusGenTx' / 'unsealShelleyTx' /
'UnsealException' all become unused.

Deletes:
  - Cardano.Wallet.Primitive.Ledger.Shelley.unsealShelleyTx
  - Cardano.Wallet.Primitive.Ledger.Shelley.UnsealException
  - cardano-api 'TxInMode' import in primitive
  - cardano-api 'toConsensusGenTx' import in network-layer

Adds 'unsafeReadTx' to the re-export of 'SealedTx' in
Cardano.Wallet.Primitive.Types.Tx. Step 1 of SealedTx decommission
plan. One fewer caller of 'cardanoTxIdeallyNoLaterThan'; the
submission path no longer touches cardano-api.

Replace mkUnsignedTx + mkByronWitness/mkShelleyWitness with
mkLedgerTx + mkByronWitnessLedger/mkShelleyWitnessLedger in
the duplicated test module.

All 8 golden hex string tests pass — ledger-native construction
produces byte-identical CBOR to the cardano-api construction.

Alternative to Transaction.hs that builds transactions using
mkLedgerTx (ledger lenses) instead of Cardano.Api.TxBodyContent.

Implements mkTransactionLedger and constructUnsignedTxLedger with
key-witnessed withdrawals and certificates. Minting, script
witnesses, and reference scripts are TODO.

Remaining cardano-api dependencies (with TODOs):
- signTransaction takes Cardano.NetworkId
- sealWriteTx roundtrips through cardano-api
- certificateFromDelegationAction returns Cardano.Certificate

Replace InAnyCardanoEra Cardano.Tx with EraValue Read.Tx as the
decoded transaction field. The CBOR bytes remain the canonical
representation.

Temporary cardano-api reconstruction functions kept for callers
that haven't migrated yet (cardanoTxIdeallyNoLaterThan,
getSealedTxBody, getSealedTxWitnesses). These deserialize from
bytes on demand.

fromSealedTx in Sealed.hs becomes trivial: just reads the field.