refactor(sdk): operatorContractUtils type safety

[teogeb]

• use bigint type when a number is a wei amount
• use EthereumAddress type for contract addresses
• use Signer instead of Wallet
  • this allow us to use client.getSigner() as an argument

Other changes

• rename some methods which are used only for test setup:
  • generateWalletWithGasAndTokens() -> createTestWallet()
  • setupOperatorContract() -> setupTestOperatorContract()
  • deployOperatorContract() -> deployTestOperatorContract()
  • deploySponsorshipContract() -> deployTestSponsorshipContract()
  • getProvider() -> getTestProvider()
• remove some obsolete parameters from these methods and from getTestAdminWallet() (not used by any component)
• do not export transferTokens() from operatorContractUtils.ts (it is an internal helper method)

Future improvements

• Refactor the utilities so that we can use sponsor/stake/delegate etc. methods both for in production environment and in tests
  • e.g. token parameter for transferTokens should be required or injected from the context (now it is implicitly test token)
• Maybe merge setupTestOperatorContract() and deployTestOperatorContract()
• Maybe deployTestOperatorContract() could return client's Operator instance?

[harbu]

In a strict sense, I don't mind the contract addresses being just plain strings here since EthereumAddress type comes with the lower casing requirement which is not strictly necessary here. However I'm not against using it here either so I'm fine with that change.

[harbu]

We don't always want to spend time waiting for a wallet to be generated that contains tokens, therefore I like the old name since it indicates what kind of wallet we are generating. Sometimes in tests we have wallets that don't need to tokens or gas (just generate random private key), need only gas (use KeyServer) or need both (use this function). I think the name should indicate that we are now generating a certain kind of wallet.

[teogeb]

Maybe it would make sense to modify dev-chain-fast so that they KeyServer keys have also some tokens. Then this utility function would be obsolete. https://linear.app/streamr/issue/ETH-800/dev-chain-fast-mint-data-tokens-for-pre-baked-accounts