Optimizations:

- Previously, if a transaction was reverting, EstimateGas would exhibit worst-case behavior and binary search up to the max gas limit (~40 state-clone + tx executions). This change allows EstimateGas to return after only a single unconstrained execution in this scenario.
- Uses the gas used from the unconstrained execution to bias the remaining binary search towards the likely solution in a simple way that doesn't impact the worst case. For a typical contract-invoking transaction, this reduces the median number of state-clone+executions from 25 to 18 (28% reduction).

Cleanup:

- added & improved function + code comments
- correct the EstimateGas documentation to clarify the gas limit determination is at latest block, not pending, if the blockNr is unspecified.