[serialize] Expose zip file alignment calculation functions (#43531)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43531
It's useful for building some tooling out of tree to manipulate zip files in PyTorch-y way
Test Plan: contbuild
Reviewed By: houseroad
Differential Revision: D23277361
fbshipit-source-id: e15fad20e792d1e41018d32fd48295cfe74bea8c
