Extract the run number for a CORSIKA log file

A fix is implemented for extracting the CORSIKA log file. I took advantage and also refactored the function and added tests for it. I made sure that the functionality before/after the refactoring stayed the same.

The issue is, I couldn't figure out how to test this with submitting an actual job. The changes are in tool_box.py which is called by cta_prod_managedata.py and therefore my local changes are not propagated to the job running the worker node. I think this is because that part is run in the pilot and not my local code, but I am not sure. May I ask for your help @natthan.pigoux, @arrabito in testing it "in production"?