Decompress history data for testing assertions

[bernt-matthias]

Fixes #11521

Currently (text) test assertions are not applicable to compressed data.

With this change test data will be decompressed before testing content assertions if the decompress keyword is given in the parent output or element.

TODO:

• test (in particular file size assertion.. )
  • the tests are in a separate commit since they are otherwise difficult to spot due to the rewrite of the assertion unit test

How to test the changes?

(Select all options that apply)

• 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

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.

[bernt-matthias]

I added tests. Quite happy with it now.

I verified that it is possible to specify assertions for compressed and decompressed content of an output (by specifying it multiple times in a test .. otherwise we would have needed to execute the test multiple times).

I was wondering:

• the assertion function takes bytes as input (which should be correct)
• but in the unit tests strings are used

Can / should we fix this? Would this by uncovered by mypy if the tests would be type annotated?

[github-actions]

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