fix(wasm-utxo): authenticate legacy PSBT prevout UTXO data

[ralph-bitgo]

What

• get_output_script_and_value_for_network (new, in
  psbt_wallet_input.rs) now authenticates PSBT input UTXO data:
  non_witness_utxo.compute_txid() must equal the prevout txid, and
  witness_utxo must match the referenced non_witness_utxo output
  when both are present. Dash and Zcash follow network-specific txid
  rules and are validated separately.
• Legacy P2SH and p2shP2pk inputs now require the full previous
  transaction on networks whose sighash does not commit the input
  amount (BTC/LTC/DOGE/DASH/Pearl, per
  Network::requires_prev_tx_for_legacy_input), enforced in
  add_wallet_input_to_psbt,
  add_replay_protection_input_to_psbt, add_input_at_index,
  BitGoPsbt::deserialize, hydration (HydrationUnspent gains an
  optional prevTx field, wired through the JS/WASM boundary) and the
  descriptor input builder (add_input_with_descriptor).
• The same validation runs before signing, parsing and fee-based
  extraction: sign, sign_with_privkey, sign_all_with_xpriv,
  sign_single_input_with_xpriv, musig2 context creation,
  parse_transaction_with_wallet_keys, and the extract_tx* family,
  so the absurd-fee guard and fee display consume authenticated values.
• Dash PSBT deserialization verifies the preserved raw prevout bytes
  against the prevout txid (compute_dash_txid).
• Nested-segwit P2SH inputs stay usable with witness-only UTXOs (via
  redeem_script/final_script_sig shape checks); forged metadata that
  merely resembles nested segwit does not bypass the requirement.
• Tests: Rust regressions in psbt_wallet_input.rs and dash_psbt.rs;
  new TypeScript suite test/fixedScript/legacyUtxoAuthentication.ts;
  AcidTest and the fixed-script suites now build synthetic previous
  transactions whose computed txids match their outpoints.

Why

WCN-1907:
the legacy sighash commits only the scriptCode, not the input amount,
so a fabricated non_witness_utxo from a compromised UTXO feed could
inflate the displayed input value, pass the absurd-fee guard, and
produce valid signatures that burn the difference to miner fees.
BIP174 requires signers to verify the prevout txid; the repo's own CLI
already did (cli/src/psbt/add_input.rs), but no library signing path
did. Value-committing networks (Zcash ZIP-243, BCH-family FORKID,
segwit, taproot) are unaffected and keep witness-only inputs.

Test plan

• Regenerate the checked-in AcidTest-generated PSBT fixtures
  (test/fixtures/fixed-script/, cli/test/fixtures/...,
  packages/webui/src/fixtures/...) — their synthetic prevouts
  predate this change and now fail txid authentication.
• cd packages/wasm-utxo && cargo test (new
  prevout_authentication_tests, test_dash_psbt_*, and existing
  suites).
• npm test in packages/wasm-utxo (new
  legacyUtxoAuthentication.ts + updated fixedScript suites).

Note: this sandbox had no Rust/Node toolchain, so the diff is
unverified: it compiles unproven and fixtures are not yet regenerated.
Draft is pushed for toolchain-backed CI and follow-up fixture
regeneration.

Ticket: WCN-1907

[linear-code]

WCN-1907