- async lock during nonce sequencing + gas estimation
- simplified cancelTransaction (still exported) such that the new transaction is populated using populateTransaction, so that all gas and fees are reset
- moved reverting contract function into its own testing helpers module, and refactored any tests to use it
- updated the test helper reverts to check EstimateGasErrors
- combine ensureNonceSequence into populateTransaction
1. rename helpers to testing and expose externally via `import pkg/ethers/testing`
2. Change detection of revert from `EthersError` to `JsonRpcProviderError`
3, Remove catch of `CatchableError` from revert detection as this would swallow errors. Update tests accordingly.