Local testnet simulation currently waits 5 seconds when starting each
individual Geth instance. Waiting a shorter amount saves almost a minute
per minimum + mainnet CI finalization job.
Measured startup times per Geth: Linux ~100ms, macOS Intel ~300ms.
The ports for the concurrently executing REST and Minimal testnet clash,
leading to some CI failures since #3827 introduced further concurrency.
Adjusting the ports to be distinct across various tests should fix this.
* Add support for launching Geth and Nimbus-eth1 nodes in launch_local_simulation
* Prevent undefined variables errors when Nimbus and Geth are not launched
Co-authored-by: Nikolay Mitev <github@hmel.org>