Summary:
Also:
- Move ProxyAgent to from app/server/utils to app/server/lib, which is
the more usual place for such classes.
- Refactor a helper (delayAbort) that node was reporting a leak in.
Test Plan: Added a test case, and tested manually.
Reviewers: JakubSerafin
Reviewed By: JakubSerafin
Subscribers: JakubSerafin, paulfitz
Differential Revision: https://phab.getgrist.com/D3897
