Add Lazy<T> spec and catalog scopes

[sergiimk]

Introduces a new type of injectable:

struct Impl {
  lazy_a: Lazy<Arc<dyn A>>,
}

Lazy<T> delays the value creation from catalog until it's requested:

let a = self.lazy_a.get()?;

Lifetime of A in this case is still controlled by the Scope (e.g. could be a Singleton and reuse an instance), so user code is expected to get() instances and let them drop ASAP after use.

Lazy values will be created using a cloned instance of a catalog that Lazy<T> stores during its instantiation alongside the Impl instance.

In cases like DB transactions this is not great, as we may need a flexibility to add transaction dynamically into a chained catalog after the Lazy<Transaction> was created, yet Lazy will be bound to an instance of Catalog that doesn't have the transaction.

To solve this I'm introducing the idea of a task-local current catalog:

catalog.scope(async move {
  // Lazy::get() will use scoped catalog
  // Catalog::current() to access catalog in current scope
}).await