[People Service] Fix issue in AOSP people service where `setupUser` in the...

[People Service] Fix issue in AOSP people service where `setupUser` in the People DataManager is stuck

Due to a missing `break` statement, People DataManager `setupUser` gets stuck at `userData.loadUserData()`, which prevents important listeners from registering properly. Among other things, this prevents the conversation widget from showing recent conversations.

This CL fixes and adds tests for the proto conversion flow.

Bug: 246928516
Change-Id: I929e1989761c8234c252b935afbe63712e93e124