`performance.timeOrigin` was being set from when JS started executing,
but `op_now` measures from an `std::time::Instant` stored in `OpState`,
which is created at a completely different time. This caused
`performance.timeOrigin` to be very incorrect. This PR corrects the
origin and also cleans up some of the timer code.
Compared to `Date.now()`, `performance`'s time origin is now
consistently within 5us (0.005ms) of system time.
![image](https://github.com/user-attachments/assets/0a7be04a-4f6d-4816-bd25-38a2e6136926)