Refactor: `updateERC721TokenRisks` and add missing `_assignAsset` tests

[NouDaimon]

• build: add missing _assignEscrowedERC1155Asset tests
• build: _assignEscrowedERC721Asset tests
• build: add exposed_assigneEscrowedERC721Asset function
• style: reorder improts
• fix: update names of _updateSingleERC1155TokenRisk tests
• build: _updateSingleERC721TokenRisk tests
• build: update comments on updateERC721TokenRisks test
• style: reorder updateERC721TokenRisks tests
• build: update comments for updateERC1155TokenRisks test
• style: reorder updateERC1155TokenRisks imports
• build: _updateSingleERC1155TokenRisk tests
• build: add _updateSingleERC1155TokenRisk and _updateSingleERC721TokenRisk to test setup
• build: expose _updateSingleERC1155TokenRisk and _updateSingleERC721TokenRisk functions
• refactor: add _updateSingleERC721TokenRisk function and use in _updateERC721TokenRisks