feat(experiment): a run's settings decide which devices of setup.yaml it uses

Closes #62 (closed) (lib side; option b: one setup, the module names the devices a configuration uses).

• @cli.needs(config) -> names | None; python -m <module> --devices --config <file> prints {"devices": [...]} (null = all) and connects nothing.
• The manifest carries chooses_devices, so a caller knows it may ask.
• Setup.only(names) / apply_setup(devices=...): only those devices' benches (and this machine's) must be set up; an unused bench's address no longer stops the run.

Bench side next: serve and share-check only the named devices.