Improve Graph testing coverage

[bitbeckers]

Case

The Graph repo is now set up with a minimal testing suite for the most common events. The coverage report today prints:

Handler 'handleAllowlistCreated' is tested.
Handler 'handleApprovalForAll' is not tested.
Handler 'handleClaimStored' is tested.
Handler 'handleInitialized' is not tested.
Handler 'handleLeafClaimed' is not tested.
Handler 'handleOwnershipTransferred' is not tested.
Handler 'handleTransferBatch' is not tested.
Handler 'handleTransferSingle' is tested.
Handler 'handleURI' is not tested.
Handler 'handleValueTransfer' is tested.
Handler 'handleValueTransfer' is tested.

Action

Add test cases for not tested handlers or, if not used, remove handlers.