test: mock store_cashu_transaction in credit_balance unit tests

The three credit_balance unit tests mock the DB session but let
credit_balance call the real store_cashu_transaction_with_retry, which
opens its own session against the global engine. In CI that database has
no cashu_transactions table; since storage failures now propagate
(a60b04ae) instead of being silently swallowed, the tests failed with
sqlite3.OperationalError. Patch the audit store like the existing
propagation test already does.

tests/unit/test_wallet.py

@@ -613,7 +613,8 @@ async def test_credit_balance() -> None:
             "routstr.wallet.recieve_token",
             return_value=(1000, "sat", "http://mint:3338"),
         ):
-            amount = await credit_balance(token_str, mock_key, mock_session)
+            with patch("routstr.wallet.store_cashu_transaction", AsyncMock()):
+                amount = await credit_balance(token_str, mock_key, mock_session)
             assert amount == 1000000  # converted to msat
             assert mock_key.balance == 6000000  # Should be updated after refresh
             # Verify atomic operations were used
@@ -636,7 +637,8 @@ async def test_credit_balance_constrains_redemption_to_key_mint() -> None:
     receive = AsyncMock(return_value=(1000, "sat", key_mint))
 
     with patch("routstr.wallet.recieve_token", receive):
-        await credit_balance("cashuAtoken", mock_key, mock_session)
+        with patch("routstr.wallet.store_cashu_transaction", AsyncMock()):
+            await credit_balance("cashuAtoken", mock_key, mock_session)
 
     receive.assert_awaited_once_with(
         "cashuAtoken", destination_mint=key_mint, destination_unit="sat"
@@ -1503,7 +1505,8 @@ async def test_credit_balance_msat_unit_not_converted() -> None:
             "routstr.wallet.recieve_token",
             return_value=(1_000_000, "msat", "http://mint:3338"),
         ):
-            amount = await credit_balance("cashuAtest", mock_key, mock_session)
+            with patch("routstr.wallet.store_cashu_transaction", AsyncMock()):
+                amount = await credit_balance("cashuAtest", mock_key, mock_session)
 
     assert amount == 1_000_000
     assert mock_session.commit.called