fix(reflection): correctly/consistently handle errors from reflection api

[pavelgj]

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 @pavelgj, 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 resolves an issue where an unintended newline character was being appended to the JSON output of action run streams. By switching to a more explicit JSON marshaling and writing process, the change ensures that the stream's response contains only the intended JSON data, improving the correctness and predictability of the API for consumers.

Highlights

• Newline Character Removal: The pull request modifies the action run stream handler to prevent an unwanted newline character from being sent at the end of the JSON response.
• JSON Encoding Method Change: The method for encoding JSON responses has been updated from json.NewEncoder(w).Encode() to a manual json.Marshal() followed by w.Write(data), providing more control over the output.
• Error Handling for JSON Marshaling: New error handling has been introduced for the json.Marshal operation, ensuring that marshaling failures are caught and an appropriate ReflectionError is returned.

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[gemini-code-assist]

Code Review

This pull request aims to fix an issue where an extra newline character is appended to the end of a streaming action response. The change correctly replaces json.NewEncoder(...).Encode() with json.Marshal() followed by w.Write() to avoid the unwanted newline. While the main change is correct, I've found a potential bug in the new error handling logic and provided a suggestion to fix it.