go-kit/log's logfmt formatter only supports emitting a particular set of types when emitting keys and values.

If a key's type is not supported, it results in that key-value pair being dropped from the log line altogether. If a value's type is not supported, it is emitted as the string unsupported value type.

It would be great if loggercheck could detect when an unsupported type is passed to go-kit/log.

I might be able to put together a PR for this, if you're open to that.