feat: PDF Handler

[KSkwarczynski]

Pull request description

This introduce PDF Handler which is suppsoed to handle Data,MC predictions. For now is only a struct to not have too many objects in SamplePDF. In future I think we could move many of converting arrays to TH1 into class. Making it real prediction class.

I didn't want to spend too much time as I am unsure whether people like this idea or not.

Haven't checked but could have minor positive impact on performance. I intorduced this for T2K ND280 and there it helped.

Changes or fixes

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Memory and CPU Usage Summary

### Memory and CPU Usage Summary

| Metric  |     Mean    |      Max    |
|---------|-------------|-------------|
| **RAM** |   270.11 MB |   310.66 MB |
| **CPU** |     7.91 %  |    13.75 %  |

Memory Usage Plot

• Job Summary Link

You can view the memory usage plot directly in the job summary from the link above.

[EdAtkin]

This is going to get a bit messy since the proposed re-name of samplePDFX was going to be sampleHandlerX I think?

[KSkwarczynski]

On the contrary I think
You will have SampleHandler and PDFHandler while the latter deal wihth Data/MC/W2 predicitons