This commit makes sure we don't load all data into memory when doing CSV exports.
The most important change here made to the recently introduced export of chat
messages (3ea31f4). We were loading all data into memory in the first version, with
this commit it's not the case anymore.
Speaking of old exports. Some of them already use find_each, and it worked as
expected, without loading all data into memory. And it will proceed working as
expected after this commit.
In general, I made sure this change didn't break other CSV exports, first manually, and
then by writing system specs for them. Sadly, I haven't managed yet to make those
specs stable, they work fine locally, but flaky in GitHub actions, so I've disabled them
for now.
I'll be making more changes to the CSV exports code soon, those system specs will be
very helpful. I'll be running them locally, and I hope I'll manage to make them stable
while doing that work.
fbe0e4c78c