How to Extend the Fuzzer

To add additional coverage:

1. Add test case generators:

   pub fn generate_high_value_listing() -> Listing {
       // Max value, long duration, uncommon currency
   }

2. Add targeted fuzz test:

   #[test]
   fn test_fuzz_high_value_listing() {
       let listing = generate_high_value_listing();
       assert_ok!(NFTMarketplace::list(origin, listing));
   }

3. Loop over randomized sequences:

   for _ in 0..100 {
       let action = generate_random_market_action();
       let _ = apply_random_market_action(origin.clone(), action);
   }