Implement mouse keys acceleration and max speed

This change introduces a TimeSource interface and injects it into MouseKeysInterceptor to improve testability and ensure deterministic timing for mouse key acceleration logic.

screencast: http://go/scrcast/NTk5ODk1MjIyNTcwMTg4OHw5NWVhZWU5Mi1jZQ

Bug: b/414403815, b/414407715
Test: atest MouseKeysInterceptorTest
Flag: com.android.server.accessibility.enable_mouse_key_enhancement
Change-Id: I0b641791546fd9d6b965d4132a018bf2739769dd