rust: linked_list: add examples

[ojeda]

Add usage examples to rust/kernel/linked_list.rs's List.

[ojeda]

Pinging @wedsonaf in case he wants to comment (e.g. it may be too early to add usage examples if he wants to change the module, since it is a work in progress).

[wedsonaf]

I'm working on the rbtree submodule now and we may need to change the linked list for consistency. There are constraints in rbtree that we didn't have with lists but that dictate certain aspects of the solution. For example, links (prev/next) point to links themselves or the outer object? Here we had a choice, but we don't in rbtree as we're using the kernel implementation.

[devillove084]

@wedsonaf Is the linked list still inconsistent with the red-black tree to a certain extent as you said? Need to continue to improve? Is it necessary to use the kernel to implement a linked list? I hope to contribute to the community from this issue. Thank you very much.

[RoKu1]

Is this still open to take ??

[ojeda]

Is this still open to take ??

José submitted a PR as shown above (#937).