Logs print too much for byte buffers (e.g. `[u8, N]`, `vec<u8>`)

[mattkur]

We often use the debug sigil ? in tracing. For types that contain byte buffers, this expands out to [b, b, b, b, b, ... ] or vec([b, b, b, b...]). This would be okay, except that logging from OpenHCL is very slow. For example, logging over the COM3 serial port takes 3 intercepts per written byte.

So, figure out how to compact this output to take fewer bytes in the byte stream...

[jstarks]

No great ideas here.

Notes:

• Our tracing subscriber gets &dyn Debug. The only thing we can really do with that is format it--we can't downcast it to specific types to treat them specially, since the Debug vtable doesn't include any mechanism to do that.
• Even if we did, we wouldn't be able to see into composite types (struct Foo(&[u8])), which I think is the common case here.
• We could add a function hex or whatever that you could use in lieu of the sigil, which would cause a byte buffer to get formatted in a more compact way. tracing::debug!(foo = hex(foo), "message"). But again, this doesn't work for composite types.
• The tracing crate added this "valueable" concept a while ago, which allows tracing structured data however you want via additional derives. But this functionality has been marked unstable for over 3 years, so I am not inclined to take a dependency on it.