fix: use JSON serialization for array fields in spreadsheet editor

[algusarov]

Summary

• Replace comma-based join/split with JSON serialization for array fields
• Prevents corruption of array items containing commas (JSON, CSV, plain text)
• Update placeholder text to reflect JSON array format

Root Cause

The spreadsheet editor used comma-based serialization (value.map(String).join(', ') and stringValue.split(',')) which corrupted any array items containing commas. Simply opening a cell for editing would corrupt in-memory data through two-way binding.

See detailed analysis in #2740.

⚠️ Warning

This is an experimental fix that changes console UX for array-based types.

Users will now need to enter array values in JSON format (e.g., ["item1", "item2"]) instead of comma-separated values. This needs careful review to ensure it doesn't negatively impact the user experience for simpler use cases.

Closes #2740

Summary by CodeRabbit

• Improvements
  • Array input fields now use JSON array format for better data handling and display
  • Updated placeholder guidance for integer, double, boolean, and string array inputs with clear examples of proper JSON formatting syntax
  • Enhanced user experience with clearer input format expectations for array-type fields

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