Add a flag for overriding number of rows to fetch

[imalsogreg]

Addresses #933

I didn't want to add tests before seeing if the approach is something you'd be willing to merge. But if that's something you'd like, I could try to get a CockroachDB instance running in the test suite.

We did test this locally and it gets around the CockroachDB portals issue discussed in #933 (and in cockroachdb/cockroach#40195)

[mehcode]

@imalsogreg do you think explicitly closing portals for fetch_one/optional instead would work?

[imalsogreg]

@mehcode I believe so! But I wasn't able to figure out how to explicitly close a portal, or where to do that closing. Do you see how that would work?

[imalsogreg]

Closing this because we're working on a better solution :)

[Cobular]

@imalsogreg I'm running into the issue described here: cockroachdb/cockroach#40195 when trying to use sqlx with cockroachdb right now and which this was supposed to fix - any update on said better solution? I am currently using sea_orm, which uses sqlx v0.6.1.

[abonander]

We have a fix on our end merged in #2081 which should release with 0.6.2, ideally this next week.

[Cobular]

Ah fantastic, thank you so much! I'll get on sea_orm about updating it's deps once that's out.