Use CLOCK_MONOTONIC if available

[cmeerw]

Only fall back to hardcoded values if CLOCK_MONOTONIC is not defined

[cmeerw]

Should have mentioned, this fixes NetBSD (and likely other BSD) build, as NetBSD has #define CLOCK_VIRTUAL 1 and #define CLOCK_MONOTONIC 3

[DeusData]

Thank you, @cmeerw! 🙏 Nice improvement — preferring the real CLOCK_MONOTONIC constant when the platform defines it, instead of the hardcoded 6/1 fallback, is both more correct on non-Linux/macOS platforms and clears a magic-number lint warning. Behavior is identical on the platforms we already handle (macOS CLOCK_MONOTONIC==6, Linux==1). Verified locally: build clean, all 3,617 tests pass. Merging via squash — authorship preserved. Thanks!