Swap local cache library for Keruald Cache implementation

Summary:
Keruald Cache code was actually based on Zed/Obsidian version,
tweaked for PSR-16.

As such, cache changes are:

• every miss returns null, no need to check for false
• serialize/unserialize are done at cache level, not calling code level

Ref T2145

Test Plan: Ensure we can still load user workspaces

Maniphest Tasks: T2145

Differential Revision: https://devcentral.nasqueron.org/D3865