Refactor email repository and query handling

Replaced `IMailRepository` with `IReceivedEmailRepository` to improve modularity and functionality. Updated `IReceivedEmailRepository` to make the `EmailAccount` parameter optional in the `FindAsync` method.

Added `ReceivedEmailRepository` with advanced filtering capabilities, including account, flags, text, UID, date, and recipient filters. Implemented deferred materialization for recipient filtering due to EF Core limitations.

Registered `IReceivedEmailRepository` in dependency injection. Updated `ReadEmailQueryHandler` to use the new repository. Improved query performance by applying filters conditionally.

src/infrastructure/DigitalData.MessagingService.Infrastructure/DependencyInjection.cs

@@ -66,6 +66,8 @@ public static class DependencyInjection
 
         services.AddScoped(typeof(IRepository<>), typeof(Repository<>));
 
+        services.AddScoped<IReceivedEmailRepository, ReceivedEmailRepository>();
+
         // AutoMapper - Register entity self-mappings (T -> T) for generic repository
         services.AddAutoMapper(config => config.AddMaps(typeof(EntitySelfMappingProfile).Assembly));