[main issue] Dynamic Devnet Management for Testing

[ndr-ds]

We recently added the ability of running arbitrary sized networks. This enables us running devnets for much cheaper, as well as having more concurrent devnets for testing (props to @christos-h for this work!).
This is a task to keep track of the different potential work that this enables.

• Add support to easily spin up and tear down a small devnet #2932
• Have a way of running tests against dynamic devnets #2933
• Have a way of running A/B tests against dynamic devnets #2934
• Create test suite specifically for linera-infra changes #2935