Make columns types an empty list for empty tabular data

[bernt-matthias]

trafficstars

• show number of columns https://github.com/galaxyproject/galaxy/issues/13258
  • [ ] could also be rows x cols (I.e. drop the words lines and columns) for compacter display
  • [x] empty files currently get 0 lines 1 colums?
    • [ ] @dannon mentioned that this is because there are tables with enormous numbers of columns (but I don't see this breaking since there is only a max no of lines limit, or?)
      • [ ] there is a 1MB limit in the line number estimation function, but the number of columns is taken from the properties filled by set_meta which reads MAX_LINES .. question is if we can assume that set_meta runs before set_peek?
    • [x] guess we should fix this and cover this with a test for Tabular.set_meta .. should this be an inline unit test or another way
    • [ ] not entirely sure if fix is 100% correct, since files with a single empty column are now also 0 column files. this is because the tabular datatype assumes empty lines as comments which are not used to determine empty columns
• shorter display of estimated number of lines https://github.com/galaxyproject/galaxy/issues/6506
  • [ ] also thought if K, M, G... suffixes might be nicer

How to test the changes?

(Select all options that apply)

• [x] I've included appropriate automated tests.
• [ ] This is a refactoring of components with existing test coverage.
• [ ] Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• [x] I agree to license these contributions under Galaxy's current license.
• [x] I agree to allow the Galaxy committers to license these and all my past contributions to the core galaxy codebase under the MIT license. If this condition is an issue, uncheck and just let us know why with an e-mail to [email protected].

[jdavcs]

Assigning the 22.09 milestone. Please remove if this is premature.

[github-actions[bot]]

This PR was merged without a "kind/" label, please correct.