Add load and loads to type stubs

[mdboom]

The load and loads methods aren't included in the typestubs, so pyright complains when users use them:

foo.py:45:28 - error: "load" is not a known member of module "simdjson" (reportAttributeAccessIssue)

[TkTech]

Thanks! But json.load and json.loads aren't used for the pysimdjson.load and pysimdjson.loads, they have different signatures.