Machines charm-code-only refresh: automatic checks skipped

On machines, if the application is refreshed from a charm code version to a charm code version that both pin an identical revision of the workload snap, the automatic checks (
- that the deployed workload snap matches the snap pinned in the charm code [this currently always passes but this may change in the future if Charmhub adds snap resources]
- that the refresh is compatible
- pre-refresh health checks & preparations

) are skipped.

On machines, if the workload will not be refreshed, the application's refresh will (usually) be completed almost immediately. `juju refresh` refreshes the charm code on each unit concurrently and independently (https://canonical-charm-refresh.readthedocs-hosted.com/latest/juju-refresh/). Once all units' charm code is refreshed, the application's refresh is complete—the application's refresh cannot be prevented.

Start by tracing the machine refresh path described in issue #10 and compare refreshes where the old and new charm code pin the same workload snap revision. Read the linked Juju refresh semantics. Done should mean the workload-match, compatibility, and pre-refresh checks are handled according to the intended behavior, with that behavior verified by tests.

Written by the indexing model from the issue text.