Currently this code expects a "url string", rather than a proper `URL` instance, which seems completely unnecessary now. The explanation for this is, as so often is the case, "historical reasons" since a lot of this code predates the general availability of `URL`.
Given that this file represents the official API, it's difficult to avoid it becoming fairly large as we add new functionality. However, it also contains a couple of smaller (and internal) helpers that we can move into a new utils-file.
Also, we inline the `DEFAULT_RANGE_CHUNK_SIZE` constant since it's only used *once* and its value has never been changed in over a decade.
