feat!: orjson instead of simplejson to load and save JSON objects

[Martin1887]

Hello.

This pull request replaces simplejson by orjson.

The previous JSON files generated by simplejson are compatible with orjson and, indeed, they seem equal to me, so no breaking changes in this aspect.

However, the API or orjson is not compatible with the Python native json library, so orjson is required to use Lab after this change meanwhile simplejson was optional.

In a performance perspective, orjson is around 4x faster (without SWAP usage) but it uses more RAM (around the double of RAM, not a problem in the most use cases). More benchmarks would be needed in your side before merging this pull request however.

Thanks.

[jendrikseipp]

Great, thanks! I'll test when I find the time. Maybe you can try fixing the tests in the meantime.