Adds generic typesafe simple ll

[ityonemo]

just something to consider. If it's not merged, I don't mind, but I think having a typesafe (simple) option will prevent people from footgunning themselves. Also could serve as a reference for someone who wants to build their own typesafe versions for more complex situations.

[matklad]

If we do this, then type-safe version should delegate to type-erased one, instead of being a reimplementation. See https://github.com/tigerbeetle/tigerbeetle/blob/main/src/stack.zig for an example.

No strong opinion on whether std should or should not include such a type-safe wrapper, but I'd personally lean towards no, in the interesting of simplicity.

[ityonemo]

I think if you read the commentary here: https://news.ycombinator.com/item?id=43679707 it's clear that @fieldParentPtr is sufficiently confusing and not being typesafe is also a magnet for (justifiable) criticism. A typesafe impl could serve to help "teach" readers of the code:

• how to restore type safety from type erased systems
• how to use/the meaning of @fieldParentPtr

An API that is "closer to what people expect from a linked list is good" but I agree that delegation would be better. I couldn't figure out how to square the circle on the first pass but I have some ideas and may take another swipe at it later today.

[ityonemo]

thanks @matklad it was way easier than I thought, I don't know why I made things more complicated the first time around.