Handle parse error for bad head exposes list

[jaredramirez]

This PR fixes #7246

It improves the parse error message if you have an invalid exposes list in the module header. The new error is:

── WEIRD MODULE NAME in /code/proj/Main.roc ────────────────────────────────────

 I am partway through parsing a header, but I got stuck here:

    1│  module foobar []
               ^

I was expecting an `exposes` list like

    [Animal, default, tame]

To do this, I had to add a branch to handle EExposes::ListStart in the function to_exposes_report.

I originally wanted to add more context to this error message based on whether the header in question was an app or a module. However, that would've required adding additional metadata to EHeader, which seemed out of scope.

While there, I noticed the branches for EExposes::Identified and EExposes::ListEnd are the same with a TODO to split them up, so I looked into that as well. As it turns out, that would require tweaking parsing which seems out of scope, so I updated the TODO with more context and left it as is.

[jaredramirez]

Looks like in the first CI run, a test timed out:

test cli_tests::test_benchmarks::base64 has been running for over 60 seconds

I went ahead and pulled in the latest commits from main, but not sure is that would fix this timeout

[jaredramirez]

Okay @smores56, this is now ready. I ended up undoing the change to handle ListEnd problems into its own branch, because it would've required tweaking some parsing code, and that felt out of scope. I added a comment in the code and updated the PR description.

I've also run all tests, formatting, etc locally and all looks good, so this should pass CI now.

[smores56]

Thanks for the change!