The new roaring iterator used for the remap and importroaring
things could also be used for unmarshalling roaring streams,
and it's a slightly simpler design that doesn't need two passes
through the data. This patch cleans that up a bit, makes it work
better with ops logs, and uses that instead. It appears to
noticably but not immensely reduce the time imports take, but it
also gets us back down to one thing parsing roaring formats.
There are a couple of subtle changes to errors we were testing
for in various tests, and one of the fuzz tests goes away because
it was actually itself an erroneous error message -- it was reporting
the header of a roaring file as an invalid op because the op log
reader was running on the header for roaring files with zero
containers. Oops.
So with the switch to a new linter, we get a lot of new warnings,
and the majority of them are harmless probably, but a few might be
real. Variously just use _ to suppress warnings, or report errors.
There's probably things here that deserve better fixes, but we can
always revisit it.
