Propagate URL errors in verbatim parsing

[charliermarsh]

Summary

Closes #3715.

Test Plan

❯ echo "/../test" | cargo run pip compile -
error: Couldn't parse requirement in `-` at position 0
  Caused by: path could not be normalized: /../test
/../test
^^^^^^^^

❯ echo "-e /../test" | cargo run pip compile -
error: Invalid URL in `-`: `/../test`
  Caused by: path could not be normalized: /../test
  Caused by: cannot normalize a relative path beyond the base directory

[zanieb]

That was more work than I expected!

[charliermarsh]

Probably why I didn't do it in the first place >.< But it's the right thing. For some reason all the error threading in requirements-txt is sorta painful.