storageproxyd: Add watchdog to log stuck requests

Adds a background watchdog thread to the Trusty storageproxy to monitor
and log any requests that are delayed for too long. This is intended to
assist in recognizing and debugging any sources of hangs related to
servicing Trusty storage requests in Android.

Test: Add sleep() and run trusty storage tests
Bug: 266595872
Change-Id: I98dfaff0dff04f97d5c657ee131e746f63b39739