CSV/JSON output formatter

[codingwithmagga]

Description

Implement a result formatter that serializes benchmark results to CSV and JSON for further analysis and reporting.

Acceptance Criteria

• Both CSV and JSON output formats are supported
• Output format is selectable at runtime
• All fields from the result struct are included in the output
• Output is written to stdout or a specified file path

Notes

TDD — tests are written before implementation code.