test: cover cumulative input value range in CheckTxInput tests. #36686

In Consensus::CheckTxInputs, for every input coin, if either coin.out.nValue or nValueIn is out of range, the transaction is invalid. The current checktxinputs_invalid_transactions_test only cover cases with one input, so the sum nValueIn is always equal to coin.out.nValue, leaving the following mutant alive.

--- a/src/consensus/tx_verify.cpp
+++ b/src/consensus/tx_verify.cpp
@@ -189,7 +189,7 @@ bool Consensus::CheckTxInputs(const CTransaction& tx, TxValidationState& state,
 
         // Check for negative or overflow input values
         nValueIn += coin.out.nValue;
-        if (!MoneyRange(coin.out.nValue) || !MoneyRange(nValueIn)) {
+        if (!MoneyRange(coin.out.nValue) && !MoneyRange(nValueIn)) {
             return state.Invalid(TxValidationResult::TX_CONSENSUS, "bad-txns-inputvalues-outofrange");
         }
     }

https://github.com/bitcoin/bitcoin/pull/36686/commits/f8c6cd84e08043f206ca338d0ba7e4dc8bef5214 adds support for multiple inputs in the test helper.

https://github.com/bitcoin/bitcoin/pull/36686/commits/5d93087c6abbda758baf3d49c552e6dc259d5021 adds a test case with multiple valid inputs, whose sum exceed MAX_MONEY, while also having nValueIn != coin.out.nValue, killing the mutant.

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External sites

• Code coverage & benchmarks: https://corecheck.dev/bitcoin/bitcoin/pulls/36686
• Ralph review <img src=https://review.fish.foo/assets/bitcoin/bitcoin/36686.png alt="Ralph review status"> https://git.fish.foo/bitcoin/bitcoin/pulls/36686#author-ralph

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