The fallback (Switch, BSDs, anything not Windows/Linux/Android/Apple) mixed
clocks: time_now_d() read the wall clock with gettimeofday, time_now_raw()
and Instant a monotonic one, from_time_raw() didn't subtract the start time,
and time_to_unix_utc() added the timestamp to the current time instead of
the start time.
Now every non-Windows platform shares the same code, built on time_now_raw()
and time_now_unix_utc(). Those two use clock_gettime where we know it's there
and std::chrono's steady_clock/system_clock elsewhere. Instant stores a
single nanosecond timestamp, and time_to_unix_utc() (which was missing on
Linux/Android/Apple) is start time plus timestamp, like on Windows.
The time origin is now set in TimeInit() rather than lazily on the first
time_now_d(), which raced between threads. iOS never called TimeInit(), so
it does now.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
