Best Value on the Shelf

Supermarket packs come in different sizes, so the price on the label doesn't tell you which is the best deal. Comparing the price per 100 g does.

Task: write best_value(packs, k) that returns the k best-value packs.

• packs is a list of dictionaries, each with name, price (in pounds) and grams.
• Work out each pack's price per 100 g: price ÷ grams × 100.
• The best value is the lowest price per 100 g.
• Return a list of [name, price per 100 g] pairs, best value first, with each price per 100 g rounded to 2 decimal places.
• If k is bigger than the number of packs, return all of them.
• No two packs have the same price per 100 g.