Testing - Add test coverage for assistants streaming and ability to u…

[knash94]

What:

• [ ] Bug Fix
• [x] New Feature

Description:

This PR adds some new tests for assistants streaming and adds the ability to mock the responses.

[knash94]

@gehrisandro Noticed the tests are failing because the GitHub actions workflow runs a composer update which updates the rules of the linter.

I could either update the action, run a composer update + lint or just ignore for now?

[iBotPeaches]

thanks!