[GNS] Remove usage of #chainId and current selected network from AssetsContractController

[salimtb]

The function #getCorrectChainId currently falls back to the currently selected network and initializes the private property #chainId. This implicit behavior can lead to inconsistencies and unexpected results, especially in multi-network contexts.

🎯 Goal

• Remove the use of the private property #chainId
• Refactor all functions that rely on #chainId to explicitly require a chainId or networkClientId parameter