There's a flaky performance test that I wanted to fix (1). This led to a couple
changes.
1 - Add timestamp() and milliTimestamp() to datetime.zig. Reduce some code
duplication and use better clock_ids where available
2 - Change Performance API to use milliTimestamp and store a u64 instead of a
f64. While the spec says a float, Firefox deals with u64 and implicit
conversion is always available. Makes our APIs simpler.
(1) - https://github.com/lightpanda-io/browser/actions/runs/17313296490/job/49151366798#step:4:131