The execute_script-backed fetchers (_fetch_calendar_event,
_fetch_todo_item) had no unit coverage of their success branch: a
well-formed envelope whose nested lookup finds the uid should return the
matching entry merged with the <domain>_entity_id key the restore path
keys off of.

TestExecuteScriptFetchers already covers the degraded-envelope raise and
the genuine-uid-miss None paths; this adds the third case, parametrized
over both fetchers, to lock the success path and the entity-keyed
nesting against future drift.

Co-authored-by: kingpanther13 <kingpanther13@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>