Series: Tests seemed to imply that the return value must be a vector, but accept lists as well

[CrowsVeldt]

All but one of the tests check the return value of slices against a vector (the exception being number<string which checks against a set), at first I assumed this meant that the
return value was supposed to be a vector specifically, but then I realized that all the tests will
pass if given a list instead. I assume because they're both seqs?

Clearly this isn't a major issue, but I did find it quite confusing at first. Is the returned value supposed to be a vector, specifically? If so, maybe the tests should be changed. If not, than maybe it should be made explicit? Either by the tests being rewritten, or perhaps just by adding a note in the README.

[tasxatzial]

@CrowsVeldt You made a great point. Although the exercises themselves don’t involve vectors, the tests generally pass even if a solution returns a list, as the container type is often ignored in equality checks. While students are free to return any structure, we don't want to imply that they should limit themselves to vectors.

Moving forward, we'll consider your feedback as we refine existing tests. We'll close this issue soon but will likely reference it in a new issue that proposes changes to the current test structure.