op-acceptor / devnet-sdk: Introduce room to alter test scheduling

[protolambda]

Introduce room to alter the scheduling of tests based on the availability of a devnet config.

Right now, opportunistically reuse devnet across tests (applies to op-e2e stack).

Note that the Go test runner does not offer this, this is something where:

• the op-acceptor / test-runner will need to express what systems are "pending"
• the devnet SDK will need to express if a "pending" system is preferred and then exit
• the test runner can then schedule the test against the pending system.

Scheduling is difficult and may only make an impact once there are many different systems to choose from.
This feature is low-priority until this changes.

Right now, opportunistically reuse devnet across tests.