feat: Format test results as JSON

[dmdmdm-nz]

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Updated the runtest and runxctest commands:

• Test results are now serialized to JSON and written to stdout.
• Removed an unnecessary log.Info() call, which mistakenly printed the string length of the formatted struct.
• Results are now always written to stdout, even when the --log-output option is missing (previously, they were only written when this option was present).

Fixes: #573