input: Write a function to generate a Python class for an online store item that includes fields for ID, name, price, and description. The class should also include methods for converting the item to a string representation and to a dictionary.
  assert StoreItem(1, 'Laptop', 1200, 'High performance laptop').__str__()=='Laptop, $1200'
  assert StoreItem(2, 'Smartphone', 800, 'Latest model smartphone').__str__()=='Smartphone, $800'
  assert StoreItem(3, 'Tablet', 500, '10-inch tablet').to_dict()=={'item_id': 3, 'name': 'Tablet', 'price': 500, 'description': '10-inch tablet'}
  assert StoreItem(4, 'Headphones', 200, 'Noise-cancelling headphones').to_dict()=={'item_id': 4, 'name': 'Headphones', 'price': 200, 'description': 'Noise-cancelling headphones'}
output: class StoreItem:
      def __init__(self, item_id, name, price, description):
          self.item_id = item_id
          self.name = name
          self.price = price
          self.description = description
  
      def __str__(self):
          return f"{self.name}, ${self.price}"
  
      def to_dict(self):
          return {
              'item_id': self.item_id,
              'name': self.name,
              'price': self.price,
              'description': self.description
          }