Add bulk create and upsert methods to repository

Added `CreateAsync` for bulk entity creation and `UpsertAsync`
and `UpsertSingleAsync` for upsert operations in `IRepository`
and `Repository`. Improved error handling in `UpdateSingleAsync`
and `DeleteSingleAsync` by throwing `NotFoundException` when no
matching entity is found. Refactored `FindAsync` and `UpdateAsync`
for better readability and performance. Cleaned up formatting in
`DeleteAsync`.

src/core/DigitalData.MessagingService.Application/Common/Interfaces/Repositories/IRepository.cs

@@ -11,6 +11,8 @@ public interface IRepository<TEntity> where TEntity : class
     // CREATE
     Task<TEntity> CreateAsync<TDto>(TDto dto, CancellationToken cancellationToken = default);
 
+    Task<IEnumerable<TEntity>> CreateAsync<TDto>(IEnumerable<TDto> dtos, CancellationToken cancellationToken = default);
+
     // READ
     Task<TEntity?> GetByIdAsync(int id, CancellationToken cancellationToken = default);
     Task<IEnumerable<TEntity>> GetAllAsync(CancellationToken cancellationToken = default);
@@ -20,6 +22,11 @@ public interface IRepository<TEntity> where TEntity : class
     Task<int> CountAsync(Expression<Func<TEntity, bool>>? predicate = null, CancellationToken cancellationToken = default);
     Task<bool> AnyAsync(Expression<Func<TEntity, bool>> predicate, CancellationToken cancellationToken = default);
 
+    // UPSERT
+    Task<(TEntity Entity, bool Created)> UpsertAsync<TDto>(Expression<Func<TEntity, bool>> predicate, TDto dto, CancellationToken cancellationToken = default);
+    
+    Task<(TEntity Entity, bool Created)> UpsertSingleAsync<TDto>(Expression<Func<TEntity, bool>> predicate, TDto dto, CancellationToken cancellationToken = default);
+
     // UPDATE
     Task UpdateSingleAsync<TDto>(Expression<Func<TEntity, bool>> predicate, TDto dto, CancellationToken cancellationToken = default);
     Task<int> UpdateAsync<TDto>(Expression<Func<TEntity, bool>> predicate, TDto dto, CancellationToken cancellationToken = default);