use lazy state initialization to avoid eager deref calculation

[aem]

h/t @gmcnaughton for pointing out that we can optimize this hook with a lazy state init to avoid double-calculating the deref on every render, which can be meaningful for expensive derefs

TODOs

• [x] linter, checker, and test are passing
• [ ] any new public modules are exported from src/GeneralStore.js
• [ ] version numbers are up to date in package.json
• [ ] CHANGELOG.md is up to date