fix(ai)!: replace ChatSession class with interface

[hsubox76]

Export a simpler public ChatSession interface representing the properties and methods of ChatSession that we want to make public and document. This is a breaking change.

This prevents us having to export the ChatSessionBase class and other implementation details of the ChatSession class that users don't need and just causes clutter in the docs.

The only drawback is that users don't have access to the class itself in order to do instanceof comparisons, but we are betting that is a rare use case.

[changeset-bot]

🦋 Changeset detected

Latest commit: 2f7ed3e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@firebase/ai	Minor
firebase	Minor

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[github-actions]

Vertex AI Mock Responses Check ⚠️

A newer major version of the mock responses for Vertex AI unit tests is available. update_vertexai_responses.sh should be updated to clone the latest version of the responses: v17.0

[github-actions]

Changeset File Check ✅

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[gemini-code-assist]

Code Review

This pull request refactors the @firebase/ai package to export a ChatSession interface instead of a class, removing the ChatSessionBase class from the public API and updating the documentation and API reports accordingly. The feedback highlights that the new ChatSession interface is missing the getHistory() method, which was previously available on the class, and recommends adding it back. Additionally, the reviewer suggests updating the JSDoc of the internal ChatSessionImpl class from @public to @internal and ensuring the API report is updated to include the getHistory() method.