[kairos] Prevent network usage before builder activations

This fixes a potential race condition where kairosNetwork.activateSpec /
transact could be invoked before Dagger-registered KairosActivatable are
activated. This can cause early access to uninitialized Events + States,
which will cause a crash.

The solution is to wrap KairosNetwork so that usage of activateSpec /
transact internally suspend until the KairosCoreStartable has activated
all KairosActivatables.

Flag: com.android.systemui.status_bar_mobile_icon_kairos
Bug: 383172066
Test: atest
Change-Id: Ia302708d64fe61cc2052ac78143a9ce52f1ac960