test: implement repository-wide unit tests

[brech1]

Description

This PR implements unit testing for several modules. The majority of methods that didn't required a circuit mock were covered. Modules like runtime and compiler are almost entirely tested.

The untested methods could be tested through integration tests, or through some testing utils with mocks in a future PR.

The workflow actions have been updated to include a testing coverage report.

There has also been some codebase structure updates.

Two bugs have been fixed:

Declaration of constant signals in the compiler module

let node = Node::new_with_signal(id, value.is_some(), false);

The order of value.is_some() and false was switched. This was declaring every constant signal as an output signal, and not setting it as constant.

Signal substitution (found by @voltrevo)

Expression::Call { .. }
| Expression::InfixOp { .. }
| Expression::PrefixOp { .. }
| Expression::Number(_, _) => {
    // Get the signal identifiers and connect them
    let given_output_id = ctx.get_signal_id(&lh_access)?;
    let gate_output_id = get_signal_for_access(ac, ctx, signal_gen, &rh_access)?;

    ac.add_connection(gate_output_id, given_output_id)?;
}
_ => return Err(ProgramError::SignalSubstitutionNotImplemented),

If a signal was assigned to a value using a Call, PrefixOp or Number this was being ignored, so these values have been added to substitution case match. The program error SignalSubstitutionNotImplemented has also been implemented.

Changes

• Implements new codecov report in CI.
• Implements unit tests for multiple modules.
• Ignores ./vscode settings.
• Removes default bin config in cargo.toml.
• Updates circuit input to be ./input/circuit.circom.
• Removes examples folder and put those circuits in the test directory.
• Removes ml-tests folder and put those circuits in the test directory.
• Restructures integration tests module.
• Adds IndexOutOfBounds integration test @curryrasul.

Related Issues

• Resolves Implement unit tests for basic features #11
• Resolves Compiler doesn't show error to a bad circuit #71

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 97.21254% with 24 lines in your changes missing coverage. Please review.

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Files	Coverage Δ
src/arithmetic_circuit.rs	90.51% <ø> (ø)
src/cli.rs	90.00% <100.00%> (ø)
src/compiler.rs	77.44% <100.00%> (ø)
src/main.rs	0.00% <ø> (ø)
src/program.rs	97.67% <100.00%> (ø)
src/circom/parser.rs	70.00% <66.66%> (ø)
src/circom/type_analysis.rs	66.66% <66.66%> (ø)
src/process.rs	63.73% <98.57%> (ø)
src/runtime.rs	91.49% <96.48%> (ø)