Verify that `VideoStream` playback works with newest-first gRPC proxy mode

[emilk]

We have a gRPC proxy mode where we send chunks to the viewer in reverse order (newest first).

Does this work with VideoStream?

Note that there are two types of issues to worry about:

• Individual chunks being "unordered" (not all timelines increasing monotonically with RowId)
• Chunks arriving out-of-order

I believe the only problem we have with VideoStream is related to the FIRST of these issues, and that the --newest-first mode doesn't affect it at all - but let's verify.

Related

• Add options to gRPC proxy server to replay _newest_ data first #11118
• Video play broken with time ranged links #10843