They follow C# conversion rules, but differ from our `bigint` module
conversions:
1. String must be big-endian.
2. Sign extension is 4-bit in size (single hex character)
and not 8-byte.
Removed unreachable code, see
8fed383523
runtime.CheckHashedWitness can only be used for transaction
verification, the other two options from reference implementation (block
and consensus payload) have separate methods for verification.
We should store each GAS record as
{
Key: ContractID + RecordsPrefix + RecordID,
Value: RecordValue,
}
So don't use state.GASRecord for storing anymore. However, it's still
useful to cache GasRecord values by using state.GASRecords, because we
have to keep GASIndexPairs sorted by indexes.
