Alfonso Subiotto Marqués

This PR is now ready for a review again. Everything is green apart from the benchmarks. The main changes since the initial PR are: - Coerce dictionary encoded utf8view values...

> Am I right in thinking for you use case you will always be passing an Arrow target DataType? No. The datafusion `VortexOpener` converts to the preferred arrow target type....

> I didn't think DataFusion handled dictionary / other encodings that weren't == the declared schema? Or am I out of date here? You're right, but that's taken care of...

I'm also on PTO this week so won't be very reachable but I think most of the urgency comes from some changes @brancz is working on so I'll defer to...