-X importtrace to supplement -X importtime for loaded modules

I’ve started drafting the PR and there are two small issues with this approach:

  1. Users might already be spelling the option -X importtime=true (or with any string). since the value is currently unchecked. This would technically break backwards compatibility; we’re retroactively constraining valid option usage.

  2. It’s unclear how to validate the corresponding environment value PYTHONPROFILEIMPORTTIME: should we error if this isn’t “1” or “2”? Should we only enable cached import tracing if the value is “2”?

While I initially thought augmenting this flag was the best approach, I think adding a new one could markedly simplify these issues :frowning: