fix: enhance OpenAI streaming events with new response types and handling (gpt-5.5)

[gaki2]

Background

When using gpt-5.5, the OpenAI streaming response included additional event types such as response.created, response.in_progress, and response.content_part.added. These events were not fully supported in the current stream handling logic, which caused the response flow to break and resulted in errors.

Changes

• Added support for newly observed OpenAI streaming event types:
  • response.created
  • response.in_progress
  • response.content_part.added
  • response.content_part.done
• Updated streaming handling in the OpenAI language model implementation to safely ignore non-output lifecycle events and correctly initialize text output when response.content_part.added is received
• Adjusted related stream tests to reflect the updated event sequence
• Included minor cleanup changes from formatting and clippy fixes

Expected Result

• gpt-5.5 streaming responses are handled correctly
• Text output starts at the proper point in the event flow
• The previous runtime error caused by unhandled response events no longer occurs
  Closes #[issue_number]

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist

• I have read the Contributing Guidelines.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• Any dependent changes have been merged and published in downstream modules.

[gaki2]

Hi @ishaksebsib . Could you review my PR?