[Proposal] Add `Optional` (default `None`) to Node classes

## Proposal

Some classes have attributes that are not required for building a Node.
For example, we don't need the `NodeSize.bandwidth` argument to create a new node. Only the `id` is necessary. But we still have to instanciate the `NodeSize` class with `bandwidth=None` since it's a required argument.
It could be possible to add a default `None` value to each optional argument to make things simpler when using Sizes/Images/Locations.

首先检查 Node 类，尤其是 NodeSize，以及提案中提到的 Sizes、Images 和 Locations 类。确定哪些构造函数参数是可选的，并验证无需显式传入这些值即可实例化节点，同时 id 等必需属性仍然是必要的。

由索引模型根据 Issue 内容生成。