Support directory (go package) execution

[fredrikaverpil]

Why this change?

• Makes execution of all tests in a folder (or the entire suite) a lot faster. Only runs one go test command. Could potentially and hopefully lay the foundation for implementing a similar or the same behavior when running all tests in a file.
• Aims to help us get there for #23

What was changed

• When running all tests in a folder (from e.g. the summary window), run just one go test command.
• Parse go test output and map the test name to the Neotest node id, return status, output and errors per Neotest node id.

Notes

• There's a bunch of stuff missing and cleanup needed, but some tests are passing on my end now.
• The timeout in the (configurable) arguments might have to be addressed somehow, as you could time out more easily now in a large project.
• It so far looks promising; might be able to use the same logic for when running all tests in a file.
• There are failing commits in this branch, will clean up later.

Try it out

Set the branch:

-- lazy.nvim
return {
  {
    "fredrikaverpil/neotest-golang",
    branch = "rnd-run-testfolder-populate-statuses",
  },
}

[fredrikaverpil]

I'm concluding the discovery process here, and closing this PR in favour for #32