Forbid assertions in release builds (assert!, panic!)

[teh-cmc]

I cannot think of any legitimate use case for release assertions for Rerun in non-test code. We never want the viewer to crash, nor the SDK.

The existing clippy machinery doesn't seem capable of differentiating between app code and test code, unfortunately.

Update: build scripts, compile-time code and other codegen shenanigans are another example where it's fine.

[Wumpf]

Related to:

• Forbid unwrap() in our code #6330