Compatibility with recent versions of Noir and minor restructuring

[ax0]

This PR brings the library in line with recent Noir versions (>=0.22.0), specifically:

• The Nargo.toml file was modified, including a change of convention for the package name.
• A bitwise & function for Field elements was added to helpers.nr and used in the function multiAnd.
• Functions that specifically depend on the choice of field (BN254's scalar field in our case) have been marked with the #[field(bn254)] attribute.
• The visibility of various functions have been specified. As it stands, only verify is marked pub.

In addition, the example provided in the README has been put in its own directory (example) and the project restructured as a workspace. The Go code generating test data and the README have been modified appropriately.

[p4u]

please @lucasmenendez review