[SR] Add StorageGroup abstraction (#68279)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/68279
While reworking the liveness analysis, I noticed that using `std::pair<size_t, std::vector<Tensor*>>` to represent storage groups made things quite unreadable.
Add a simple class to wrap a `std::vector<at::Tensor*>` and store a `size` attribute
Test Plan:
`buck test caffe2/benchmarks/static_runtime/...`
Also ran inline_cvr benchmarks, did not see any errors
Reviewed By: swolchok
Differential Revision: D32369447
fbshipit-source-id: e0b562aa7eefd738b1a34f1f37eb7bc95d71a257
