When a seek is requested while a previous seek is still blocked waiting
for not yet available bytes, we want to abandon the old request
immediately and start processing the new one.
This first pass only applies to the following two cases:
- Public functions returning a view type into an object they own
- Public ctors storing a view type
This catches a grand total of one (1) issue, which is fixed in
the previous commit.
DecoderError::formatted() made a ByteString, took a view into it,
dropped the ByteString, then propagated the (now invalid) view back to
the caller as an error.
Since the object has to keep the ByteString alive, keep it as a variant
to make sure the "happy" path with no alloc remains alloc-free.
