Scoru: Add example kernel for sequencer

Context

This one improves Makefile by compiling sequencer with --release and targeting WASM.

Also, it adds an example empty kernel which I would like to use in e2e tests. Hopefully it's ok for now just add it to lib.rs, let me know if there is a better place for it.

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR