Currently, `size` is cached in `SampleMetadata` when samples are committed in `SampleQueue`, which worked because we didn't support reading files with `CryptoInfo`. This change prepares for future `CryptoInfo` support, as the size changes when reading samples with encrypted data. Caching the size at commit time could lead to incorrect buffer `size` calculations.
Existing tests verify the correctness of the `getSampleSize()` API.
PiperOrigin-RevId: 700714178
52e45e0864