Change power hint rate limiter to use max interval instead of max queue

Using a max interval between hints instead of a max queue size to force
batches better reflects the need to avoid having our hint session go
stale as well as the fact that higher refresh rates can accumulate more
hints before needing to send them.

Bug: b/195990840
Test: manual
Change-Id: I7cffc75e962c42f50952dd02f5c148d8573ea97e