Fix a race condition in remote access HAL.

We should not delete ClientContext after we TryCancel it since the
reader in the main task loop might still access it, e.g., while
calling reader->Finish. We must wait under reader->Finish is
returned, then to delete the ClientContext.

This CL also updates README.md to incorporate soong namespace change.

Test: manually test on sdk_car_x86_64-userdebug
Run TestWakeupClientServer
Run --set-ap-state 1 0 and then --set-ap-state 0 0 multiple times.
Bug: 261234399

Change-Id: I3b0c632546c218c4ced43af95a585cd41e0da036