Fix BackProgressAnimatorTest AssertionError flakiness

It's not 100% clear what causes the flakiness. This CL fixes 3 potential
root causes for the flakiness:
1. The timeout is increased in order to give the system enough time to
   finish the animation even under heavy load.
2. The BackProgresssAnimator is reset in the tearDown method to prevent
   it from affecting later test cases.
3. The progress equality check is now robust for floating point
   calculation imprecision.

Bug: 426069482
Test: BackProgressAnimatorTest
Flag: EXEMPT test fix
Change-Id: I5c5da140e5c71d131cde77cad9f62328c5ad6844