Optimize EstimateGas API

[trinhdn2]

Resolve issue #390

EstimateGas repeatedly executes a transaction, performing a binary search with multiple gas prices to determine proper pricing. Each call retrieves a new copy of the state https://github.com/tomochain/tomochain/blob/76420ee3ba79120351018b86c1a84c4001ad9064/internal/ethapi/api.go#L1136
Because the pending/latest state can be changed during the execution of EstimateGas, this can potentially cause strange behaviors. EstimateGas currently conducts a binary search to determine a suitable gas limit for a tx, and continues searching with a higher gas limit whenever the transaction's execution results in revert. While this makes sense if the reason for revert is out of gas, increasing the gas limit is highly unlikely to allow a non-OOG reverting transaction to succeed (unless it is making unusual use of the GAS opcode).

This PR modifies EstimateGas to retrieve the state once and use a copy of it for every call invocation it does. This has two benefits:

• Saves compute overhead.
• Eliminates a race condition where a reverting transaction causes the gas limit lowerbound to increase repeatedly during gas estimation, only for a state change to allow the transaction to later succeed later in the loop, resulting in an unreasonably high estimate being returned. (We believe this is happening in practice in one of our applications)

[trinhdn2]

Superseded by #409