## Issue Addressed
Resolves#3159
## Proposed Changes
Sends transactions to the EE before requesting for a payload in the `execution_integration_tests`. Made some changes to the integration tests in order to be able to sign and publish transactions to the EE:
1. `genesis.json` for both geth and nethermind was modified to include pre-funded accounts that we know private keys for
2. Using the unauthenticated port again in order to make `eth_sendTransaction` and calls from the `personal` namespace to import keys
Also added a `fcu` call with `PayloadAttributes` before calling `getPayload` in order to give EEs sufficient time to pack transactions into the payload.
## Issue Addressed
N/A
## Proposed Changes
Preemptively switch Nethermind integration tests to use the `master` branch along with the baked in `kiln` config.
## Additional Info
There have been some spurious timeouts across CI so this also increases the timeout to 20s.
## Proposed Changes
Recently, changes to Nethermind's Kiln branch have broken our integration tests.
This PR updates the chainspec to Kiln to ensure proper compatibility.
## Issue Addressed
NA
## Proposed Changes
This PR extends #3018 to address my review comments there and add automated integration tests with Geth (and other implementations, in the future).
I've also de-duplicated the "unused port" logic by creating an `common/unused_port` crate.
## Additional Info
I'm not sure if we want to merge this PR, or update #3018 and merge that. I don't mind, I'm primarily opening this PR to make sure CI works.
Co-authored-by: Mark Mackey <mark@sigmaprime.io>
