Pure Nargo CLI functions

[michaeljklein]

Description

Problem*

Test nargo's primary commands (check, compile, ..) without touching the filesystem.

Summary*

TODO:

• test against example json file
• make example json file unit test case

Each CLI command has a run function.

This PR splits that function into run and run_pure, where run reads/writes files and run_pure does everything else.

It also adds Serialize/Deserialize impl's for FileManager and Workspace, to allow specifying an entire workspace as a single json file. (Enable with --features "fm/serde nargo/serde")

Additional Context

I attempted to implement a pure version of verify but it has two stages of pure execution (compile, read inputs, then verify) which got complex so leaving it and test out for now: check/compile/execute are the focus of most tests I'm looking at anyway.

Example application

Dumping all compilation test cases as json:

pub fn compile_workspace_full_pure(
    workspace: &Workspace,
    workspace_file_manager: FileManager,
    compile_options: &CompileOptions,
) -> Result<(ExpressionWidth, Vec<CompiledProgram>, Vec<CompiledContract>), CliError> {

    // this is added
    use std::fs::OpenOptions;
    use std::io::prelude::*;

    let mut file = OpenOptions::new()
        .create(true)
        .write(true)
        .append(true)
        .open("test_cases_compile.json")
        .unwrap();

    writeln!(file, "{:?}", serde_json::to_string(&(workspace, workspace_file_manager.clone())).unwrap()).unwrap();

Documentation*

Check one:

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

PR Checklist*

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