feat(client, broker): [NET-1310] Use custom event polling logic for Broker features

[teogeb]

Moved OperatorContractFacade and operatorContractUtils from the broker package to the client package. Renamed it to Operator. Added StreamrClient#getOperator semi-public method to the client API.

Modified the class to use client's contract utilities, e.g. the FallbackProvider and the ChainEventPoller.

• The functions of operatorContractUtils don't use FallbackProvider and the ChainEventPoller. That's maybe ok as those are used in tests only. But if we start to use the functions in production code, we should start to start to use the helper classes also in these functions.

Future improvements

• Replace individual contract artifacts with imports from @streamr/network-contracts-ethers6. But need to find a way to do this without bloating webpack bundle size.
• Could use https://typedoc.org/tags/hidden/ in classes/methods which are currently marked as @deprecated?
• Do we need to export the _operatorContractUtils object? Maybe could add a StreamrClient#getSponsorship method? Some methods/functions of Operator and operatorContractUtils could be moved to the class returned by that method
  • Maybe could remove OperatorRegistry class?
• Lazy load instances of Contract in Operator?