Avoid copying data in `RecordReader.{read,search_for}_message()` by creating a `memoryview` object instead of `bytes`.
Avoid copying data in `RecordReader.{read,search_for}_message()` by creating a
`memoryview` object instead of `bytes`.

This is compatible with `FromString()` methods of message classes nowadays.

PiperOrigin-RevId: 347865053

google/riegeli,google/riegeli,google/riegeli,google/riegeli