Cardano Updates

Replace cardano-api round-trip with direct Read.Tx era projection via
Meta.getMetadata . Meta.getEraMetadata. Drops the four callers of
cardanoTxIdeallyNoLaterThan in this file (the cardano-api re-decode
was only used to feed getTxBody/txMetadata).

No behavioural change: the ledger metadata path is what Server.hs and
DB.TransactionInfo already use.

Introduce sealedTxWitnessCount :: SealedTx -> Int, counting VKey
plus bootstrap witnesses via 'addrTxWitsL'/'bootAddrTxWitsL' on the
stored 'EraValue Read.Tx'. Byron txs counted as 0 (wallet doesn't
construct them through SealedTx).

Migrate Server.hs's two 'length $ getSealedTxWitnesses sealedTx'
sites (redeemer and witness accounting) to use it. Drops
'getSealedTxWitnesses' from Server.hs's import list.

Step 2b of SealedTx decommission plan.

Replace compareOnCBOR's roundtrip through cardano-api
(cardanoTx → Cardano.serialiseToCBOR) with the raw bytes
already stored in SealedTx.serialisedTx. Identical
comparison outcome, one fewer caller of
cardanoTxIdeallyNoLaterThan. Step 1 of SealedTx
decommission plan.

Five-step plan to remove the three remaining Cardano.Api imports from
lib/primitive/lib/Cardano/Wallet/Primitive/Types/Tx/SealedTx.hs by
eliminating the bridge functions (cardanoTxIdeallyNoLaterThan,
cardanoTxInExactEra, sealedTxFromCardano*, getSealedTxBody,
getSealedTxWitnesses, cardanoApiTxToReadTx).

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.

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