Tweak retrospective computation of change & outs

Without this change integration tests would fail e.g. where:

```pseudo-code
constructTx
  paymentTo addr1 (0 ada)

  |
  |
  V

Tx
  output: addr1 (1 ada) -- min ada, set automatically
  output: addr2 (9 ada) -- change
```

as we'd believe both outputs in the resuling tx were change -- neither
of them exists in the original output list.

If there are 'n' outputs in the original unbalanced tx, we will with
this commit instead judge that the first 'n' are "outputs" and that the
ones after that are all change. While this makes assumptions about how
balanceTx appends outputs, it is more importantly ressilient to outputs
being modified, like with the `increaseZeroAdaOutputs` feature.

lib/wallet/api/http/Cardano/Wallet/Api/Http/Shelley/Server.hs

@@ -2467,34 +2467,30 @@ constructTransaction
 
  singleton x = [x]
 
- toUnsignedTxChange initialOuts = \case
+ toUnsignedTxChange = \case
  WalletOutput o ->
  let address = getApiT (fst (o ^. #address))
  derivationPath = fmap getApiT (o ^. #derivationPath)
  coin = Coin.fromQuantity (o ^. #amount)
  assets = getApiT (o ^. #assets)
- txChange = TxChange address coin assets derivationPath
- txOut = TxOut address (TokenBundle coin assets)
  in
- if txOut `L.notElem` initialOuts then Just txChange else Nothing
+  TxChange address coin assets derivationPath
  ExternalOutput _ ->
- Nothing
+ error "constructTx.toUnsignedTxChange: change should always be ours"
 
- toUnsignedTxOut initialOuts = \case
+ toUnsignedTxOut = \case
  WalletOutput o ->
  let address = getApiT (fst (o ^. #address))
  coin = Coin.fromQuantity (o ^. #amount)
  assets = getApiT (o ^. #assets)
- txOut = TxOut address (TokenBundle coin assets)
  in
- if txOut `L.elem` initialOuts then Just txOut else Nothing
+  TxOut address (TokenBundle coin assets)
  ExternalOutput o ->
  let address = getApiT (fst (o ^. #address))
  coin = Coin.fromQuantity (o ^. #amount)
  assets = getApiT (o ^. #assets)
- txOut = TxOut address (TokenBundle coin assets)
  in
- if txOut `L.elem` initialOuts then Just txOut else Nothing
+  TxOut address (TokenBundle coin assets)
 
  toUsignedTxWdrl p = \case
  ApiWithdrawalGeneral (ApiT rewardAcc, _) amount Our ->
@@ -2523,9 +2519,17 @@ constructTransaction
  , unsignedInputs =
  mapMaybe toUnsignedTxInp (decodedTx ^. #inputs)
  , unsignedOutputs =
- mapMaybe (toUnsignedTxOut initialOuts) (decodedTx ^. #outputs)
+ -- HACK: we leverage that balanceTx will append change outputs after
+ -- the initial outputs to tell them apart. 'List.\\' does not work
+ -- when balanceTx may change ada-quantities of initial inputs.
+ take (length initialOuts)
+ $ map toUnsignedTxOut (decodedTx ^. #outputs)
  , unsignedChange =
- mapMaybe (toUnsignedTxChange initialOuts) (decodedTx ^. #outputs)
+ -- HACK: we leverage that balanceTx will append change outputs after
+ -- the initial outputs to tell them apart. 'List.\\' does not work
+ -- when balanceTx may change ada-quantities of initial inputs.
+ drop (length initialOuts)
+ $ map toUnsignedTxChange (decodedTx ^. #outputs)
  , unsignedWithdrawals =
  mapMaybe (toUsignedTxWdrl path) (decodedTx ^. #withdrawals)
  }