[bugfix] use the right staking api client

[drohit-cb]

What changed? Why?

Looks like in the last rebase, I ended up incorrectly choosing the wrong stake api client while calling broadcast_staking_operation.

Testing

1. Added unit tests for the newly added function which I missed the last time.
2. Tested SDK locally

[27] pry(main)> wallet = Coinbase::Wallet.create(network: :ethereum_holesky)
=> Coinbase::Wallet{id: 'f253b29f-3f6b-426f-93c2-80300f533301', network_id: 'ethereum_holesky', default_address: '0x9a423EA007a38AaF90D84c4eb0D4dc258B49f211'}
[28] pry(main)> wallet.faucet
=> Coinbase::FaucetTransaction{transaction_hash: '0xad1e4859c7da1442062580823ecb1956ab835a4dc91a9ed8aef465bada3f6412', transaction_link: 'https://holesky.etherscan.io/tx/0xad1e4859c7da1442062580823ecb1956ab835a4dc91a9ed8aef465bada3f6412'}
[32] pry(main)> wallet.balances
=> {:eth=>0.1e-1}
[33] pry(main)> staking_operation = wallet.stake(0.00001, :eth)
=> #<Coinbase::StakingOperation:0x000000014b1cb488
 @model=
  #<Coinbase::Client::StakingOperation:0x0000000107034960
   @address_id="0x9a423EA007a38AaF90D84c4eb0D4dc258B49f211",
   @id="f488c865-2152-4bef-95bb-84ef3e93128c",
   @network_id="ethereum-holesky",
   @status="complete",
   @transactions=
    [#<Coinbase::Client::Transaction:0x0000000107034e88
      @from_address_id="0x9a423EA007a38AaF90D84c4eb0D4dc258B49f211",

Qualified Impact

[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
Reviews	✅ 1/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

Approved review 2255933626 from marcin-cb is now dismissed due to new commit. Re-request for approval.