Fix the extract_along_coords() docstring for accuracy and clarity

[ayshih]

This PR fixes the fact that the extract_along_coords() docstring doesn't explain accurately or clearly what it is doing. Most notably, it falsely claims that it extracts "every pixel the coordinate path intersects". See also #6815.

Fixes #6815

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout 4.0
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 bccad31049a3ab20fdacc630a3a6362808f182e1

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #6819: Fix the `extract_along_coords()` docstring for accuracy and clarity'

4. Push to a named branch:

git push YOURFORK 4.0:auto-backport-of-pr-6819-on-4.0

5. Create a PR against branch 4.0, I would have named this PR:

"Backport PR #6819 on branch 4.0 (Fix the extract_along_coords() docstring for accuracy and clarity)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.