Introduce `llvm-cov` into debugger infra

It should be done in both compiler and debugger, and it enables a few things:
- tracking test coverage
- enables profiling/fuzzing of the contracts
- PGO
- ...
cc @bitwalker @greenhat

Look at the existing debugger and compiler codebases to understand how instrumentation is added. Research how llvm-cov integrates with Rust projects via LLVM tooling. Determine what changes are needed in both the compiler and debugger to emit and consume coverage data. Check for existing tests or examples of coverage tooling in the project.

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