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

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**

Start by locating AssetsContractController and its getCorrectChainId function, then trace every function that reads the private chainId or the currently selected network. Refactor those entry points to require chainId or networkClientId explicitly, and verify that no implicit selected-network fallback or private chainId usage remains.

Written by the indexing model from the issue text.