Functions: Add in function streaming

[AustinBenoit]

Description

Provide details of the change, and generalize the change in the PR title above.

Functions: Add in function streaming

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Testing

Describe how you've tested these changes.

Ran the test locally in unity editor and created a new integration test

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Type of Change

Place an x the applicable box:

• Bug fix. Add the issue # below if applicable.
• New feature. A non-breaking change which adds functionality.
• Other, such as a build process or documentation change.

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[gemini-code-assist]

Code Review

This pull request introduces Server-Sent Event (SSE) streaming support for callable functions in the Firebase Unity SDK, adding the StreamAsync API and a new StreamResponse class, along with corresponding integration tests and dependency updates. The review feedback highlights two important improvements in HttpsCallableReference.cs: first, the HttpResponseMessage returned by SendAsync should be disposed to prevent connection leaks when using HttpCompletionOption.ResponseHeadersRead; second, a null check should be added for response.Content before reading the stream to avoid potential null reference exceptions.

[AustinBenoit]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces support for Callable Functions Streaming in Firebase Functions via the new StreamAsync API, utilizing Server-Sent Events (SSE). It includes the implementation of StreamResponse to represent intermediate messages and final results, SSE stream parsing logic, and corresponding integration tests. Feedback on the changes suggests improving the streaming implementation by properly disposing of HttpRequestMessage, combining cancellation tokens, and ensuring responsive cancellation during stream reads.