Refget Sequences start/end query parameter and range request corner cases

The specification is not explicit as to whether clients must use either both or neither of `start=…` and `end=…` query parameters, or if just one of them may also be used. If it is permissible to use `start=…` by itself or `end=…` by itself, the specification is not explicit about what that should mean.

The specification does not specify what should happen when a request contains an `end` query parameter larger than the total sequence length. Reasonable behaviours could be to return a sub-sequence from `start` to the end of the sequence (i.e., “clipping” the `end` value) or to fail with `Bad Request` (as the requested `end` is out of bounds).

Note that the specification does say that out of bounds Range requests must fail with `Bad Request`. However this is inconsistent with [RFC 7233](https://datatracker.ietf.org/doc/html/rfc7233#section-2.1), which specifies that out of bounds `last‑byte‑pos` is to be clipped while out of bounds `first‑byte‑pos` is unsatisfiable so should fail.