Improve error message when SDK is used and not initialized

[rohan-agarwal-coinbase]

What changed? Why?

• Right now when a user forgets to call Coinbase.configure, they see an unclear error message because the apiClients aren't defined. This PR uses the proxy pattern in javascript to intercept getting the apiClients, and returns a clear message to the user.

Notes to reviewers

Formatting/linting fixed a few unrelated test files so they can be ignored.

Testing

• Added a unit test to confirm error behavior when not initialized. Updated conftest for global test setup to mock the APIClients - this was needed for all existing tests to succeed with the new behavior.
• E2E testing, both with and without Coinbase.configure, have expected behavior.

Here's how it looks:

❯ python test_smart_wallet.py 
Traceback (most recent call last):
  File "/Users/rohanagarwal/code/cdp-sdk-python/test_smart_wallet.py", line 68, in <module>
    test_smart_wallet_operations()
  File "/Users/rohanagarwal/code/cdp-sdk-python/test_smart_wallet.py", line 15, in test_smart_wallet_operations
    smart_wallet = SmartWallet.create(account=owner)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/rohanagarwal/code/cdp-sdk-python/cdp/smart_wallet.py", line 61, in create
    model = Cdp.api_clients.smart_wallets.create_smart_wallet(create_smart_wallet_request)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/rohanagarwal/code/cdp-sdk-python/cdp/cdp.py", line 38, in __getattr__
    raise UninitializedSDKError()
cdp.errors.UninitializedSDKError: Coinbase SDK has not been initialized. Please initialize by calling either:

- Cdp.configure(api_key_name='...', private_key='...')
- Cdp.configure_from_json(file_path='/path/to/api_keys.json')

If needed, register for API keys at https://portal.cdp.coinbase.com/ or view the docs at https://docs.cdp.coinbase.com/wallet-api/docs/welcome

Qualified Impact

[cb-heimdall]

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