_base_hash_on_config should not be an attribute

[dachengx]

What is the problem / what does the code in this PR do

If we set __version__ of some plugins as None, error will show like: https://github.com/AxFoundation/strax/actions/runs/10564686303/job/29267605250. This is because self. _base_hash_on_config might be changed by multiple threads when multithreaded processing, while calculating _auto_version might be slow.

So this PR fixes the issue and adds a test of multithreaded processing when __version__ of some plugins as None.

Can you briefly describe how it works?

Can you give a minimal working example (or illustrate with a figure)?

Please include the following if applicable:

• Update the docstring(s)
• Update the documentation
• Tests to check the (new) code is working as desired.
• Does it solve one of the open issues on github?

Please make sure that all automated tests have passed before asking for a review (you can save the PR as a draft otherwise).

[coveralls]

coverage: 90.812% (+0.002%) from 90.81%
when pulling 06c73d7 on none_default_version
into 5192fce on master.