Protobuf 3.15 introduced support for marking scalar fields like
uint32 as optional, and all of our tooling appears to support it
now. This allows us to use simple optional/null checks in our Rust/
TypeScript code, without having to resort to an inner message.
I had to apply a minor patch to protobufjs to get this working with
the json-module output; this has also been submitted upstream:
https://github.com/protobufjs/protobuf.js/pull/1693
I've modified CardStatsResponse as an example of the new syntax.
One thing to note: while the Rust and TypeScript bindings use optional/
null fields, as that is the norm in those languages, Google's Python
bindings are not very Pythonic. Referencing an optional field that is
missing will yield the default value, and a separate HasField() call
is required, eg:
```
>>> from anki.stats_pb2 import CardStatsResponse as R
... msg = R.FromString(b"")
... print(msg.first_review)
... print(msg.HasField("first_review"))
0
False
```
6941bccde4