fix(error): use compact JSON for error output to preserve NDJSON streams

[nuthalapativarun]

Description

print_error_json was using serde_json::to_string_pretty, which produces multi-line output. This breaks NDJSON consumers (e.g. gmail +watch, events +subscribe) that expect one JSON object per line.

Changed to serde_json::to_string so errors are always emitted as a single line, consistent with the NDJSON protocol.

Closes #680

Checklist:

• My code follows the AGENTS.md guidelines (no generated google-* crates).
• I have run cargo fmt --all to format the code perfectly.
• I have run cargo clippy -- -D warnings and resolved all warnings.
• I have added tests that prove my fix is effective or that my feature works.
• I have provided a Changeset file (e.g. via pnpx changeset) to document my changes.

[changeset-bot]

🦋 Changeset detected

Latest commit: 2c84f41

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

This PR includes changesets to release 1 package

Name	Type
@googleworkspace/cli	Patch

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[gemini-code-assist]

Summary of Changes

Hello, 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 an issue where error messages were being emitted as multi-line JSON, which disrupted consumers expecting NDJSON format. By switching to compact serialization, the CLI now ensures that each error is represented as a single line, maintaining protocol consistency for streaming tools.

Highlights

• JSON Serialization Update: Updated the error reporting mechanism to use compact JSON serialization instead of pretty-printing, ensuring compatibility with NDJSON stream consumers.
• Regression Testing: Added a new test suite to verify that all error variants are serialized as single-line strings, preventing future regressions in stream compatibility.

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[gemini-code-assist]

Code Review

This pull request modifies the error printing logic in the Google Workspace CLI to output compact JSON instead of pretty-printed JSON, preserving NDJSON stream compatibility. It also adds a unit test to verify that all error variants serialize to a single line without newline characters. I have no feedback to provide as the changes are clean and well-tested.