Add 2025 and 2026 data datasets

[jomatthi]

This PR builds the campaigns for the 2025 and 2026 Nano v15 Data datasets. Since the current recommendation is to use the 2024 MC datasets for both Eras, the 2024 campaign is copied and only the Data datasets are exchanged.

[jomatthi]

Hi @riga Sorry for the noise! I think I managed to find all the typos now. At least the checks are happy. Let me know if you want me to change anything else!

[riga]

Thanks @jomatthi !

I went through the changes and I only have three comments:

1. The datasets you called data_jethtmet_* were usually called data_met_* in previous eras, including 24_v15.
2. Likewise, data_egamma_* was usually called data_e_*.
3. In the campaign definitions, I think we should try to use the transfer_datasets helper mechanism rather than starting from a full copy of the 24 campaign. This would prevent changes added to the latter from unknowingly proliferating into the other campaigns.

Could you apply 1 and 2? I could contribute point 3 :) (edit: Done)

[jomatthi]

Thanks @riga
I've implemented 1 and 2 in the latest commit.
I've not worked with the data_met_* datasets before so I didn't know. For the data_egamma_* there is at least a convention change between v12 and v15, see my comment on PR #102 . But I agree to stay consistent in the v15 files.

And thanks for providing that transfer_datasets functionality 👍