Fix flaky monotonic time.
Fix flaky monotonic time.

This change ensures that even platforms with some TSC issues (e.g. KVM),
can get reliable monotonic time by applied a lower bound on each read.

PiperOrigin-RevId: 309773801

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor