Implements Python error hint when importing from src.

[dom96]

Test is in EW because wd-test doesn't make it easy to assert on script startup failures afaik.

Test Plan

$ bazel test //src/edgeworker/tests/python:python-src-import-error.ew-test_0.26.0a2@ --test_tag_filters=-none --cache_test_results=no

[codspeed-hq]

CodSpeed Performance Report

Merging #5407 will not alter performance

_{Comparing dominik/src-import-better-error (206f59a) with main (3527891)}

Summary

✅ 33 untouched
⏩ 9 skipped¹

Footnotes

1. 9 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[hoodmane]

To avoid memory leaks you should do:

try:
   raise exc
finally:
   del exc

Or ideally move the whole thing into a Python try/catch.
It's important to remember that exceptions hold references to frame objects so keeping them alive also keeps all the local variables from all those scopes alive.

[hoodmane]

What about if the import happens in the fetch handler?

[hoodmane]

This will raise an attribute error if exc doesn't have a name attribute. You need to check if it's a ModuleNotFoundError.

[hoodmane]

If the test suite is currently passing let's make sure there's a test where some other error is raised at top level and make sure it doesn't get messed up.