feat: compile stdin and fuzz

[michaeljklein]

Description

Problem*

My previous attempt to use AFL to fuzz nargo got stuck on making a fuzzing target:

• There's a lot of file accesses
• The file manager is opaque and challenging to fuzz directly
• A quick-and-dirty JSON encoding of the file manager was too fragile to fuzz with
• Removing file accesses directly was hard

Summary*

This attempt rethinks the problem:

• Instead of fuzzing a whole workspace or package, only main.nr is fuzzed
• This is done by adding a debug CLI option to accept main.nr from STDIN and use an implicit Nargo.toml

Results thus far:

• It works, but it's rather slow (~1.72 executions/s)
  • Even with test cases restricted to 120 bytes!
  • ~95% of compilation appears to be parsing
• There appears to be remaining file accesses, with only ~90% stability achieved

Additional Context

Documentation*

Check one:

• [x] No documentation needed.
• [ ] Documentation included in this PR.
• [ ] [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist*

• [x] I have tested the changes locally.
• [ ] I have formatted the changes with Prettier and/or cargo fmt on default settings.