Add tests for withdraw functionality in StreamContract

[Obiajulu-gif]

This pull request enhances the test coverage #82 the StreamContract by adding tests for the withdraw function, specifically focusing on authorization scenarios. The new tests ensure that only authorized recipients can successfully withdraw from a stream, and that unauthorized attempts are properly rejected.

Authorization testing:

• Added withdraw_succeeds_for_authorized_recipient test to verify that a recipient with proper authorization can successfully withdraw from a stream and that the authorization is correctly recorded. (contracts/stream_contract/src/test.rs)
• Added withdraw_fails_for_non_recipient_and_authorized_call_still_succeeds test to confirm that unauthorized users cannot withdraw, and that an authorized recipient can still withdraw after a failed unauthorized attempt. (contracts/stream_contract/src/test.rs)

Test utility improvements:

• Utilized MockAuth and MockAuthInvoke for simulating contract authorization in tests, improving the realism and robustness of test scenarios. (contracts/stream_contract/src/test.rs)

Closes #82

[ogazboiz]

Great addition of tests for the withdraw functionality. This is much needed. Approving and merging.

[Obiajulu-gif]

@ogazboiz merge it

[ogazboiz]

Thanks for the PR. This seems to be identical to #117 and only adds 'extern crate std;'. I'll leave this for now until we decide if that addition is globally necessary or if it was part of a larger change.

[Obiajulu-gif]

i have fix the issue @ogazboiz

[ogazboiz]

These two test lines are a very small addition. To make this PR merge-worthy, please consider: 1) Adding at least a few more test cases for the withdraw flow (e.g. unauthorized withdraw, withdraw more than deposited), and 2) Rebasing on latest main which has seen significant changes since this PR was opened.

[ogazboiz]

These test lines are a small but good start. To make this ready for merge, please consider adding a few more test cases for the withdraw flow (e.g., edge cases like unauthorized access or over-withdrawal) and rebasing on the latest main branch.