feat(service): add ReadLastUsedReceiverNameByMail method to IEnvelopeReceiverService and EnvelopeReceiverService

- Added `ReadLastUsedReceiverNameByMail` method to `IEnvelopeReceiverService` interface.
- Implemented `ReadLastUsedReceiverNameByMail` method in `EnvelopeReceiverService` to retrieve the last used receiver's name by email and handle results with `DataResult`.

EnvelopeGenerator.Application/Services/EnvelopeReceiverService.cs

@@ -122,5 +122,11 @@ namespace EnvelopeGenerator.Application.Services
             var dto_list = _mapper.MapOrThrow<IEnumerable<EnvelopeReceiverDto>>(er_list);
             return Result.Success(dto_list);
         }
+
+        public async Task<DataResult<string?>> ReadLastUsedReceiverNameByMail(string mail)
+        {
+            var er = await _repository.ReadLastByReceiver(mail);
+            return er is null ? Result.Fail<string?>().Notice(LogLevel.None, Flag.NotFound) : Result.Success(er.Name);
+        }        
     }
 }