Let's support at least reading "b3" header from a single string, most commonly traceid-spanid-1
It would also be nice to support optionally writing this, especially in message providers or others with constrained environments.

Expected behavior

As discussed on openzipkin/b3-propagation#21 and first implemented here: https://github.com/openzipkin/brave/blob/master/brave/src/main/java/bra

In our codebase, we push RequestContext and immediately run some code with try-with-resources.
For example:

try (SafeCloseable ignored = ctx.push()) {
    logger.trace(decorate(msg));
}

If RequestContext provides run(Runnable) or call(Callable) we can reduce boilerplate code and simplify it.

ctx.run(() -> logger.trace(decorate(msg));

This is inspired by g

Unused imports are included in the headers of generated files causing 2.12 builds with the default -Yfatal-warnings` setting to fail (unless the correct linting options are unset)

Expected behavior

Scrooge generates files with headers including only the imports the current file needs.

Actual behavior

Scrooge generates import statements for classes that are never used.

St