Test cpu_time_reasons with process cycles

Add a couple testcases to verify the propagation of cpu_time_reasons
over bindings in a cycle where multiple different reasons may be
propagated.

Added a fluent helper utility for flag asserts and used it to create a
fluent helper for verifying various process attributes.

Refactored CPU_TIME and IMPLICIT_CPU_TIME asserts to be much more
readable using the new helper methods.

Fixed flaky reason checks in testUpdateOomAdj_UidIdle_StopService.

Test: atest FrameworksMockingServicesTests:MockingOomAdjusterTests

Flag: EXEMPT tests only

Bug: 429283517
Change-Id: I4b48752c0e51219435e6d3278d697dc05e55ed34