Consider custom JSON-library

[thomasht86]

Both requests and httpx uses the json-library for serialization/deserialization, and I think that it might be justified to switch to a more effective json loader.

See

• https://www.reddit.com/r/Python/comments/1ah4d2t/my_first_ever_article_finding_the_fastest_python/
• https://dollardhingra.com/blog/python-json-benchmarking/
• https://jcristharif.com/msgspec/benchmarks.html