Cache can cause schmas to not be built

If you run `packageDaffodilBin` and something goes wrong (e.g. schema compilation failure, typo in sbt configuration) it might not generate a saved parser. But the `FileFunction.cached` function the plugin uses to look for changes and determine if it needs to rebuild the parser doesn't know this--it thinks everything finished successfully. So running the command again won't do anything--it won't compile the schema and it won't error. It just thinks there's no work that needs to be done.

I think `FileFunction.cached` is supposed to handle this, so we might be using it incorrectly.

Start by tracing the packageDaffodilBin command to the FileFunction.cached call and reproduce a failed schema compilation or sbt-configuration typo. Confirm that no saved parser is produced and that rerunning currently skips the work; done means the failure is reported and a subsequent run retries schema compilation.

Written by the indexing model from the issue text.