Edited POWHEG using parallel generation and manyseeds

[jackal1-66]

• POWHEG generation is now split into chunks (default 1e4 events). This should be helpful especially on hyperloop (where the generator was first requested). The program will be configured only once, creating the needed files which later will make the simulation faster at each iteration. The .lhe filename is updated at every step inside Pythia.
• A fix to improve macros changes detection linked to ini files has been pushed

[github-actions]

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[jackal1-66]

The CI didn't trigger the test of the various POWHEG generators. Checking what the issue might be

[jackal1-66]

After the fix, the ini files seems to be grepped correctly from local and lxplus tests. Waiting for new CI results

[jackal1-66]

Still not tested on the CI. Debugging...

[jackal1-66]

CI now gets correctly the files to be tested. There are some ini files with some issues on the CI, however they were tested locally (also in docker mode) and they work perfectly fine. This PR can be merged