Issue #6300 - Fix nested schema parsing in insert_rows

[adamf]

Hi! Here's a potential fix for handling JSON serializing of nested schema in BigQuery (issue 6300).

I think before accepting this it would need tests, but I wanted to hear the maintainer's thoughts on the location of the fix (client.py or _helpers.py). Also, I'm sure there's a better way to do this, but I needed a fix for this problem in my project :)

Closes #6300

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[adamf]

I signed it!

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CLAs look good, thanks!

[tswast]

Thanks for the PR!

I've requested a few changes in the review comments, but I'll actually handle these today. I appreciate your efforts and want to respect your time. We require 100% unit test coverage, so it'll probably be easier for me to tackle the refactor and unit testing.

[tswast]

I've updated the PR to move the added methods to _helpers.py with names matching the existing *_to_json functions in that module. I've updated existing unit tests to cover the new logic.

[WillianFuks]

I was also working on a fix for the issue but ended up being too late as it seems lol.

Still, did some unit tests and system tests, maybe those can also be useful. For system tests I used the same issue as the one observed in the bitcoin table and now it's working :). Won't do PR as it doesn't seem necessary, the issue seems already fixed by now.

[adamf]

Thanks @tswast ! Appreciate the fixes and tests!