trunk/9de9a266fb1f4eda32ada8fdee55cd0325b09553: Expose approximate-clock helpers for the CUPTI monitor (#186035)

Expose the pieces the experimental monitor needs to share the same time

model as the stock profiler.

This adds Python bindings for the approximate clock, the

ApproximateClock-to-Unix-time converter, and the native CUPTI timestamp

callback entry point so monitor-collected activities can be normalized

and exported in the same wall-clock domain as CPU profiler events.

Pull Request resolved: #186035

Approved by: https://github.com/dolpm, https://github.com/scotts