input: Write a python function to determine if a field exists in a database table and return its type.
  assert check_field_exists('Machine_item', 'unusable')==('BooleanField', True)
  assert check_field_exists('Machine_item', 'mac1')==('MacField', True)
  assert check_field_exists('Machine_item', 'nonexistent_field')==(None, False)
output: def check_field_exists(table_name, field_name):
      from django.apps import apps
      try:
          model = apps.get_model('your_app_name', table_name)
          field = model._meta.get_field(field_name)
          return (field.get_internal_type(), True)
      except LookupError:
          return (None, False)
      except model._meta.model.DoesNotExist:
          return (None, False)