Fix: wrap list JSON output in array for parseable output

[Jah-yee]

Summary

Fixes mercury-cli issue #70.

When running commands like mercury accounts list --format json, multiple pretty-printed JSON objects were emitted back-to-back without an enclosing array or commas, making output unparseable by standard JSON parsers:

{"id": "...", "name": "..."}
{"id": "...", "name": "..."}

This change wraps JSON/pretty formatted list output in a proper JSON array with commas between items:

• Non-pager path: Prepends [\n, appends ,\n]\n to collected output
• Pager path: Writes [\n, emits items with ,\n separators, writes \n]\n

Before: {...}{...} (unparseable)
After: [{...},{...}] (valid JSON array)

Closes #70

[Jah-yee]

Fix Explanation

Bug: mercury accounts list --format json emitted multiple pretty-printed JSON objects concatenated without array brackets or commas, making output unparseable by standard JSON parsers.

Root cause: ShowJSONIterator in pkg/cmd/cmdutil.go collected formatted JSON for each item and concatenated them directly without wrapping.

Solution: Modified ShowJSONIterator to wrap JSON/pretty formatted list output in a proper JSON array with comma separators between items:

• Non-pager: prepends [\n, appends ,\n]\n
• Pager: writes [\n before streaming, ,\n between items, \n]\n after

This likely fixes all list endpoints that use the same ShowJSONIterator pattern.

[Jah-yee]

👋 Hi! Just checking in — this PR has been open 14+ days with no review. Happy to make any adjustments if needed! 🙏

[Jah-yee]

👋 Hi! Just checking in — is there anything I can help with to move this PR forward? Happy to address any feedback! 🙏

[Jah-yee]

Hi @ALL, gentle reminder that this PR is waiting for review. Happy to make any changes — just let me know! 🙏

[Jah-yee]

Friendly ping — any updates? Happy to address feedback.