Cancel remaining fields on exceptions

[mgorven]

gather() returns when the first exception is raised, but does not cancel any remaining tasks. These continue to run which is inefficient, and can also cause problems if they access shared resources like database connections.

Fixes: #236

[Cito]

Thank you @mgorven - will have a look later this week or on the weekend.

[codspeed-hq]

CodSpeed Performance Report

Merging #238 will not alter performance

_{Comparing mgorven:cancel-tasks (2821841) with main (0107e30)}

Summary

✅ 14 untouched benchmarks

[mgorven]

Check is failing because coverage is not 100%, but this is because completed = True in the test case is not executed which is exactly what we're testing for.

[Cito]

Thanks a lot for this contribution and sorry for not looking into it earlier.

Your approach looks good to me, just a few suggestions.

Also, I think we need to do something similar in other places where we gather results asynchronously, e.g. in complete_list_value(). Let me know if you want to add it to this PR or create a separate one, or whether I should work on this.

[mgorven]

Thanks for the review, I've addressed the comments. You can take the other instances, unless you aren't able to get to that for a while in which case I can help.

[Cito]

Ok, will try to do something similar for the other instances as well and then create a release in the coming days.

[Cito]

Thank you again for your contribution to this project.