Ensure JSON representation is compact. #3363

[BERRADA-Omar]

Summary

this PR solves the issues mentionned here #3363

The following related issues could all be resolved together...

We should use ensure_ascii=False for more compact text representations.
We should use separators = (',', ':') for more compact list and object representations.
We should use allow_nan=False to disallow invalid Infinity and NaN representations.

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.

[tomchristie]

Yep, thx. ☺️

[tomchristie]

I've just noticed this accidentally snuck in a private import.

@BERRADA-Omar would you be up for refactoring these tests?

We can test this against public API using httpx.Request(). Eg...

data = {...}
req = httpx.Request("POST", "https://www.example.com/", json=data)
assert req.content == ...
assert req.headers = ...