Handle namespace for models and contracts

[remybar]

Namespace feature

This PR adds the concept of namespace for world elements such as models and systems.
Namespaces will give us more flexibility to organize models and systems together, and come
with a finer-grained authorization management.

Basics

Basically, a namespace is a ByteArray which has to be registered to the world before being used.

Each world element belongs to a namespace.
By default, the namespace is the main package_id,
which is the name field specified in the package section of the Scarb.toml file.
So, for small projects, no need to worry about this namespace concept, all their models and systems will belong to the same default namespace.

But for bigger projects, this default namespace can be overriden when defining a model with #[dojo::model(namespace: "YOUR_NAMESPACE")] or a system with #[dojo::contract(namespace: "YOUR_NAMESPACE")].

To get an unique selector for a model in a namespace, the model selector is now computed using the following formula: selector = hash(hash(namespace), hash(model_name)) where hash() is the poseidon hash function. So, instead of using the selector! macro which only accepts hardcoded strings, the poseidon hash of a ByteArray is computed on the serialized ByteArray (so, an array of felt252).

Auth

Dojo Auth system works with 2 roles: Owner and Writer.
A Owner must be an account contract. It owns a resources (world, models, systems or namespaces) and can grant/revoke Owner and Writer roles to other contracts.
A Writer can be any kind of contract and has write access to a resource.

Basically, to write to a resource:

• the caller account must be
  • an owner of the world,
  • OR an owner of the resource,
  • OR has the Writer role for the resource,
• OR the caller contract must have the Writer role for the resource.

To write to a model, there is another level of authorization, so:

• the caller account must be
  • an owner of the world,
  • OR an owner of the model namespace,
  • OR an owner of the model,
  • OR has the Writer role for the model namespace,
  • OR has the Writer role for the model,
• OR the caller contract must have the Writer role for the model namespace OR the model.

In brief, having write access to a namespace gives write access to any model of the namespace.

Naming

Since model and namespace selectors are hashes of ByteArray, it is important to normalise the way these
ByteArray are stored, and especially their cases. So:

• since a model or a system name come from Cairo code, it keeps the case used in the code (mainly Pascal case in Cairo),
• a namespace must use lower case characters (a-z) and underscore (_) only,
• there is no more qualified path, each world element is identified by an unique name built by concatenating the namespace and the element name, separated by a :,
• this unique name is also used to name the related manifest file except that : is replaced by _.