time.nx

time.nx -- monotonic + wall clock, via Linux/NishiOS clock_gettime. Zero third-party runtime: only __syscall. Syscall 113 is clock_gettime(clk_id, *timespec); returns 0 on success, -1 on error. Linux RV64 numbers; NishiOS keeps the same set. TimeSpec layout matches Linux's `struct timespec`: two i64 fields, seconds + nanoseconds. `var ts: TimeSpec` stack-allocates via the compiler's alloca path; `&ts` hands the kernel a pointer to write into. Callers generally want ns since some origin: * monotonic_ns() -- ns since boot; cannot go backwards; immune to wall-clock jumps (NTP, DST, manual set). Use for timing. * wall_clock_ns() -- ns since Unix epoch; CAN jump. Use only for human-readable timestamps and inter-machine correlation.