Fix Python interpreter not found error

[seeM]

Attempts to address #5730. My hunch is that getInterpreters() doesn't wait for the Python extension to complete its discovery process, so it's possible to get there before our runtime's interpreter is discovered.

The whole point of restoring a workspace-affiliated runtime is to skip discovery. It looks like getInterpreterDetails() is a better fit, since (I think) it "resolves" an interpreter path to a PythonEnvironment independent of discovery.

QA Notes

E2E tests C609619 and C609617 should pass in CI:

• Passing E2E run: https://github.com/posit-dev/positron/actions/runs/12387951151/job/34578222238
• 10x run of both failing tests: https://d38p2avprg8il3.cloudfront.net/playwright-report-12389107722-6803/index.html. There was a single failure, but that looks like an unrelated issue.

Python and Reticulate runtimes should continue to function as expected.

[github-actions]

E2E Tests 🚀  ^?
This PR will run tests tagged with: @critical

[jmcphers]

This LGTM. I ran through the steps in #5730 and found that the new venv successfully started up when reopening the project.

[dfalbel]

LGTM! Locally tested the reticulate functionality and everything seems to work correctly.

[juliasilge]

Thank you so much! 🙌