Unverified binary generation

[hrutvik]

When testing compiler modifications we generally don't want to wait for a verified binary to be compiled in-logic. This issue is about creating an unverified binary pipeline. The idea is to translate the PureCake compiler to CakeML in-logic, and print the result to S-expressions. Then we should be able to use a pre-built CakeML binary to produce an executable PureCake compiler.

Overall:

1. Create a folder compiler/binary/unverified which prints the result of pure_compilerProgTheory to S-expressions
2. Add a Makefile in this directory for downloading the latest CakeML and compiling the S-expressions to produce a PureCake executable (borrowing from examples/Makefile)
3. Update the GitHub Actions workflow for creating a binary (.github/binary.yml) to use the unverified pathway