Constrain client ThreadStore to MinimallyEncodedRawThreadInfos

Summary: This allows us to get rid of some of the branching covered in https://linear.app/comm/issue/ENG-6070/tidy-up-flow-branching-from-minimal-permissions-work.

Test Plan: Flow, things continue to work as expected on native and web clients in my local environment.

Reviewers: ashoat, ginsu, tomek

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D10588