Call `flush()` in `Writer.__exit__` to fix the `DATA_LOSS` error messages.
Call `flush()` in `Writer.__exit__` to fix the `DATA_LOSS` error messages.

PiperOrigin-RevId: 397283390
Change-Id: I3e3f99d43db073f7da5a0e42540f10e422c8fb67

deepmind/reverb,deepmind/reverb,deepmind/reverb,deepmind/reverb