pyembed can be broken and "cargo install" doesnt care

If I have a syntax error in pyembed code, `cargo install --path pyoxidizer` will happily include it and push it into the generated projects.
I know I can manually check it, but it would be nice if the normal build process checked it.
It would be great if "pre" compiled pyembed objects were included into the generated projects to reduce build times for the generated projects.

Reproduce the issue with `cargo install --path pyoxidizer` after introducing a syntax error in pyembed code, then inspect the generated projects and their build path. Done means the normal install process detects invalid pyembed code; the request to include precompiled pyembed objects would also need a defined scope.

Written by the indexing model from the issue text.