Remove raw iCal caching and onIcalsFetched callback; simplify iCal listener flow

[ivan-lednev]

Motivation

• Eliminate storing and propagating raw iCal payloads through plugin settings and Redux to simplify iCal handling and reduce persisted state surface.
• Remove the async onIcalsFetched callback and related preloaded iCal state since raw iCal caching is no longer required.
• Clean up associated types and listeners to match the simplified iCal flow.

Description

• Removed RawIcal/raw iCal caching from settings, types, and Redux-related code and deleted the Cache/PluginData shape from settings.ts.
• Eliminated onIcalsFetched argument from createReactor and ReduxExtraArgument, made preloadedState optional in createReactor, and defaulted it to {} in store.ts.
• Removed the icalsFetched listener and related handling in listener-middleware.ts and no longer preload iCal state in main.ts, including deleting code that saved raw iCals to plugin data.
• Adjusted imports and type references throughout the codebase to drop RawIcal usages and updated variable names (initialPluginData -> initialSettings).
• Updated tests to reflect the new flow by removing onIcalsFetched fixtures and expectations in tests/integration.test.ts and tests/store/ical.test.ts.

Testing

• Ran the automated test suite (npm test), which includes unit and integration tests, and all tests completed successfully after the changes.
• Updated and executed tests/integration.test.ts and tests/store/ical.test.ts, and both updated tests passed.

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Codex Task