test(unit): add tests for utility, round_robin, and stat_trackers

[dasepmoch]

Description

Add unit tests for three modules that currently have no test coverage:

• src/utility.h — Hex conversion (util::hex, hex_vec, from_hex, from_hex_vec), string parsing (from_chars, from_view), Either type, FailGuard, buffer_t, append_struct, endian helpers, and log_hex.
• src/round_robin.h — Round-robin iterator wrap-around, arithmetic operators, comparisons, edge cases (single element, multiple cycles), and arrow operator with structs.
• src/stat_trackers.h/.cpp — Format helpers (one_digit_after_decimal, two_digits_after_decimal), min_max_avg_tracker callback timing, min/max/avg calculation correctness, reset behavior, and double type support.

These are pure-logic, header-only (or minimal .cpp) modules with zero external dependencies, making them ideal candidates for improving test coverage without needing GPU or platform-specific hardware.

Related Issues / Discussions

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (non-breaking change which improves existing functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Dependency update

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code where necessary
• My changes generate no new warnings
• New tests have been added that prove my fix is effective or that my feature works
• I have verified my changes locally (CI will verify on push)

[sonarqubecloud]

Quality Gate failed

Failed conditions
25 New issues
25 New Code Smells (required ≤ 0)

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