test(refresh): cover the manager gate and the status reconciliation (3/6)

[marceloneppel]

Issue

Part of the refresh module migration from the PostgreSQL VM and K8s charms' 16/edge branches into this library. Stacks on #264.

Solution

Covers the refresh-aware status gate (higher-priority suppression, lower-priority substitution for active statuses with the .last_refresh_unit_status.json caching, non-active statuses written directly, explicit refresh argument) and the collect-unit-status reconciliation (higher-priority status set and cached, stale cached status cleared through the set_default_status bridge or restored from the lower-priority status, unrelated statuses left alone), plus the manager construction paths: the K8s untrusted-app case disabling app status and PeerRelationNotReady leaving the refresh object unset.

Drops the file-local refresh_versions.toml fixture, now provided for every test by the conftest shunt introduced in #264. The fixture anchors its paths on the setup-time working directory so per-test chdirs cannot corrupt the teardown.

Checklist

• I have added or updated any relevant documentation.
• I have cleaned any remaining cloud resources from my accounts.