Handle alias types properly for CSV

[dominiklohmann]

📔 Description

This fixes a crash with nested aliases in the CSV reader. To reproduce, replace the definition of port in base.schema like this:

type proxy = count
type port = proxy

Then import CSV data, e.g.,

gunzip -c vast/integration/data/csv/argus-M57-10k-pkts.csv.gz | vast -N import csv

📝 Checklist

• All user-facing changes have changelog entries.
• The changes are reflected on docs.tenzir.com/vast, if necessary.
• The PR description contains instructions for the reviewer, if necessary.

🎯 Review Instructions

Commit-by-commit.

[lava]

Ideally this could use a unit test to ensure we'll not regress on this. But clearly not crashing is better than crashing, so I'm also not opposed to merging it immediately.

[dominiklohmann]

Ideally this could use a unit test to ensure we'll not regress on this. But clearly not crashing is better than crashing, so I'm also not opposed to merging it immediately.

We have this open story about possibly consolidating the data conversions to a given type (ch23655), and I think it makes more sense to add tests in the scope of that story.

I'll still try and write a minimal unit test for this one, but I'm unsure how feasible it is. I've added a minimal test for the table slice change.