[Profiler] Memory timeline to show actual timestamps (#96535)
Summary: Rather than starting the timeline at t=0, keep the actual timestamps of the memory events.
Test Plan: CI Tests
Reviewed By: leitian, chaekit
Differential Revision: D43807624
Pulled By: aaronenyeshi
Pull Request resolved: https://github.com/pytorch/pytorch/pull/96535
Approved by: https://github.com/davidberard98
