This CL also fixes EOS handling to account for not-yet-copied samples in
`remainingInputToCopyFrameCount`, which would throw off the final output
sample count calculation.
For testing, we allow a tolerance of 0.000017% drift between expected
and actual number of output samples. The value was obtained from running
100 iterations of `timeStretching_returnsExpectedNumberOfSamples()` and
calculating the average delta percentage between expected and actual
number of output samples. Roughly, this means a tolerance of 40 samples
on a 90 min mono stream @48KHz.
PiperOrigin-RevId: 683133461
af922fbcb0