Add support for reasoning text streaming events

[louisbels]

What:

• Bug Fix
• New Feature

Description:

Adds support for the new reasoning text streaming events introduced in OpenAI's Response API when using models with reasoning capabilities (like gpt-oss):

• response.reasoning_text.delta - Emitted when a delta is added to reasoning text content
• response.reasoning_text.done - Emitted when reasoning text is completed

These events are documented in the OpenAI API Reference and are used when models perform step-by-step reasoning before
generating their response.

Changes made:

• Created ReasoningTextDelta class to handle reasoning text delta events
• Created ReasoningTextDone class to handle completed reasoning text events
• Updated CreateStreamedResponse to recognize and properly parse these new event types
• Added test coverage with fixtures and test cases for both event types

Related:

N/A - Feature addition based on OpenAI API updates

[iBotPeaches]

A minor comment. You see how you include type and then typecast it as a generic string? Since we read the type prior to passing it to the child concrete class - we know the type.

So we exclude it, so it doesn't pack an object with an unneeded key. You can peek the other classes to see what I mean - https://github.com/openai-php/client/tree/main/src/Responses/Responses/Streaming

Basically remove type as we let the calling code handle/set that.

[iBotPeaches]

thanks!