feat(ci): add script to ci

The contributing guidelines are defiend as standard for Miden VM and it
is desirable it is extended here.

If we use the guidelines from the beginning, we avoid future problems
related to big refactors and history migration.

This commit introduces a script that will enforce the following
constraints:

- Tests are successful
- Rustfmt is executed for every Rust source
- Clippy warnings are resolved

The same model of Miden VM is adopted here. However, `no-std` check
wasn't added because the library, as of the moment, doesn't implement
that.

closes #3

This commit introduces a workspace structure with a `Cargo.toml`.
Currently we have a single member `crypto`, but these can be added
incrementally in the future.

Currently the API modules are hidden to the crate scope.

In order to avoid global permissive allows, they can initially be
exported, and tweaked to local scopes as they get implemented, finalized
and tested.

Related to #3

Implement basic Merkle tree-related primitives