/s

Simplify IMAP email fetching API and refactor logic

Removed `markAsSeen` parameter from `FetchEmailsAsync` and
`FetchEmailByUidAsync` methods in `IImapEmailService` to
simplify the API. Updated `MailSearchFilter` to make `MaxCount`
nullable for greater flexibility.

Removed `markAsSeen` from `FetchEmailByUidQuery` and
`FetchEmailsQuery` records and their handlers. Deleted
`FetchEmailByUidQueryValidator` as it is no longer needed.

Refactored `LimilabsImapEmailService`:
- Introduced `FetchEmailUidsAsync` to centralize UID fetching logic.
- Simplified `FetchEmailByUidAsync` using a new helper method.
- Consolidated connection, authentication, and folder selection
  into reusable private methods.
- Removed redundant code for search criteria and flag fetching.

Removed `IsSeen` from `ReceivedEmailContext` and improved
overall code readability and maintainability by reducing
duplication and centralizing logic.

src/core/DigitalData.MessagingService.Application/Common/Interfaces/IImapEmailService.cs

@@ -13,7 +13,6 @@ public interface IImapEmailService
     /// </summary>
     /// <param name="account">Account whose IMAP settings will be used.</param>
     /// <param name="filter">Filter to apply when fetching emails.</param>
-    /// <param name="markAsSeen">
     /// When <see langword="true"/> (default), fetched messages are marked as <c>\Seen</c> on the server.
     /// Set to <see langword="false"/> for a non-destructive read (uses <c>BODY.PEEK</c> internally).
     /// </param>
@@ -21,7 +20,6 @@ public interface IImapEmailService
     Task<IEnumerable<ReceivedEmailContext>> FetchEmailsAsync(
         EmailAccountDto account,
         MailSearchFilter filter,
-        bool markAsSeen = true,
         CancellationToken cancellationToken = default);
 
     /// <summary>
@@ -35,7 +33,6 @@ public interface IImapEmailService
     /// <summary>
     /// Fetches a single email by its UID.
     /// </summary>
-    /// <param name="markAsSeen">
     /// When <see langword="true"/> (default), the message is marked as <c>\Seen</c> on the server.
     /// Set to <see langword="false"/> for a non-destructive read.
     /// </param>
@@ -44,7 +41,6 @@ public interface IImapEmailService
         long uid,
         string folder = "INBOX",
         bool withAttachments = false,
-        bool markAsSeen = true,
         CancellationToken cancellationToken = default);
 
     /// <summary>