fix(typing): Resolve misc type ignores in schemapi.py

[dangotbanned]

These are all very low-priority, but allows using "python.analysis.typeCheckingMode": "basic" in this module, without any warnings.

Planning to investigate improving the peformance of validation, which will be much easier with a live type checker

[binste]

Thanks! I've also noticed that validation can take up a significant amount of time in contexts where milliseconds matter such as in web applications. In an application at work, I had to disable validation of charts when it's deployed to production. Maybe there are things in Python we could improve but I think part of it is also just how the jsonschema library works. Curious to see what you find out @dangotbanned! There are other libraries such as https://github.com/horejsek/python-fastjsonschema and https://github.com/Stranger6667/jsonschema-rs but we'd need something which is also available in pyodide and from which we can continue to produce user-friendly error messages.