fix(go): fixed panic when stream value is nil

[apascal07]

Checklist (if applicable):

• PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• Tested (manually, unit tested, etc.)
• Docs updated (updated docs or a docs bug required)

[gemini-code-assist]

Summary of Changes

Hello @apascal07, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a potential runtime panic that could occur in AI generation and prompting streaming operations when an intermediate streamValue was unexpectedly nil. It introduces a new, comprehensive IsNil utility function to robustly check for nil values across various Go types. This function is then integrated into the streaming logic to safely skip yielding nil values, thereby preventing crashes and improving the overall stability and robustness of the streaming process.

Highlights

• Robust Nil Checking: Introduced a new generic IsNil utility function in go/internal/base/misc.go that uses reflection to accurately determine if a value of any type (including pointers, interfaces, maps, slices, channels, and functions) is nil.
• Panic Prevention in Streaming: Implemented checks using the new base.IsNil function within go/ai/generate.go and go/ai/prompt.go to prevent panics. The system now gracefully skips yielding a StreamValue if the streamValue itself is nil, particularly useful for handling incomplete or unparseable outputs during streaming.
• Improved Stream Resilience: Enhanced the resilience of AI generation and prompting streams by ensuring that nil intermediate results do not lead to runtime errors, thus improving the stability of streaming operations.

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[gemini-code-assist]

Code Review

This pull request addresses a panic that occurs during data streaming when a parsed value is nil, which can happen with incomplete data like partial JSON. The fix introduces a robust base.IsNil helper function that uses reflection to correctly check for nil across various Go types. This check is then applied in GenerateDataStream and DataPrompt.ExecuteStream before yielding a streamed value, preventing the panic. The changes are logical and well-implemented. I've added one suggestion to improve test coverage for the new utility function.