examples: native objects in state

[joe-p]

This PR contains the changes to the marketplace contract that we would ideally want to see possible for TEALScript migration ease and familiarity with TypeScript devs. The main blocker for this is not supporting serialization of objects for usage in state (either as key or value). We currently get errors like the following:

contracts/marketplace.algo.ts:300:5 error: Not Supported: Serializing object to bytes
                                            this.listings(key).value = {
                                            ^~~~~~~~~~~~~~~~~~
contracts/marketplace.algo.ts:32:3 error: lib.d.ts::object is not a valid type for storage
                                           listings = BoxMap<ListingKey, ListingValue>({ keyPrefix: "listings" });

Blocked by algorandfoundation/puya-ts#129