Make genTxIn a top-level function.

The new location is next to the other general-purpose generators, such
as `genTxOut`.

lib/balance-tx/test/spec/Internal/Cardano/Write/Tx/BalanceSpec.hs

@@ -2219,9 +2219,6 @@ txWithUTxOFromPartialTx PartialTx {tx, extraUTxO} =
 
 genTxWithUTxO :: IsRecentEra era => Gen (TxWithUTxO era)
 genTxWithUTxO = TxWithUTxO.generate genTxForBalancing genTxIn genTxOut
-  where
-    genTxIn :: Gen TxIn
-    genTxIn = fromWalletTxIn <$> W.genTxIn
 
 shrinkTxWithUTxO :: IsRecentEra era => TxWithUTxO era -> [TxWithUTxO era]
 shrinkTxWithUTxO = TxWithUTxO.shrinkWith shrinkTx shrinkUTxOToSubsets
@@ -2324,6 +2321,9 @@ genTxForBalancing :: forall era. IsRecentEra era => Gen (Tx era)
 genTxForBalancing =
     fromCardanoApiTx <$> CardanoApi.genTxForBalancing (cardanoEra @era)
 
+genTxIn :: Gen TxIn
+genTxIn = fromWalletTxIn <$> W.genTxIn
+
 genTxOut :: forall era. IsRecentEra era => Gen (TxOut era)
 genTxOut =
     -- NOTE: genTxOut does not generate quantities larger than