Refactored `ReceivedEmailContext` to use `record` for immutability
and value-based equality. Added `SyncIntervalSeconds` to
`EmailAccountsOptions` for configuring IMAP sync intervals.
Introduced `EmailSyncWorker` as a background service for periodic
email synchronization. Registered `IMemoryCache` and integrated
caching in `LimilabsImapEmailService` to reduce redundant fetch
operations. Optimized `FetchEmailByUidAsync` to conditionally
handle attachments and improve performance.
Refactored logging and improved code readability by adopting modern
C# features like `record`, `with` expressions, and `IOptions`.
Performed general cleanup and streamlined method implementations.
TekH
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