fix(pluginhost): add plugin quiesce handling with safe rollback during hot reload

- Add new `plugin.quiesce` ABI method and propagate RPC error codes from plugin call failures.
- Invoke quiesce on the replaced plugin before loading a new version, then only activate replacement after quiesce succeeds.
- Improve hot-reload safety by serializing lifecycle transitions, cleaning up failed/canceled loads, and rolling back to the previous plugin state when replacement fails or is canceled.

Closes: #5134