Remuxing comparing durations needs to signal EOS

Remux test compared before/after durations after copying all samples,
but never signaled end-of-stream. Thus, leaving the 'duration' for after
up to the muxer (and subsequent extractor). This did not fare well with
newer muxer which corrected precedence between headers and sample
counts.

Bug: 355685788
Flag: TEST_ONLY
Test: atest CtsMediaMuxerTestCases
(cherry picked from https://android-review.googlesource.com/q/commit:ea984312f699edcd25ca92bb4235bcb7fc0d1f8b)
Merged-In: Iec0f338d06e94f18038294925a06b6df4e743324
Change-Id: Iec0f338d06e94f18038294925a06b6df4e743324