[PyTorch] RecordFunction: use SmallVector for ObserverContextList (#68412)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/68412
These lists have the same size as CallbackHandles, so they should be the same container type.
ghstack-source-id: 145668416
Test Plan:
Run same command as previous diff.
Before: see previous diff, average about 0.46us
After: P467928077, average about 0.43us
Reviewed By: chaekit
Differential Revision: D32454856
fbshipit-source-id: 3a3ff4d381d99f51ef868d4dec4db7c411b5ea56
