WIP: Diboson process split (ggZZ/qqZZ) and add missing Run 3 datasets

[neeraj-1729]

Summary of Changes

1. Diboson Process Split (processes/ewk.py):

   • Restructured flat zz process tree into explicit zz_qqbar ($q\bar{q}\to ZZ$) and zz_gg ($gg\to ZZ$) sub-processes.
   • All existing leaf process names (zz_zll_zll, zz_zee_zee, etc.) are preserved for backwards compatibility.
   • Updated theory inclusive cross sections:
     • 13 TeV: $16.518 \pm 1.84%$ pb (NNLO+NNLL, PhysRevD 10.1103/2rr7-5xv3, Table 1)
     • 13.6 TeV: $17.627 \pm 1.93%$ pb (NNLO+NNLL, PhysRevD 10.1103/2rr7-5xv3, Table 1)
   • Updated per-decay-mode cross sections:
     • zz_qqbar: NLO $\times k=1.15$ ($14.6625$ pb inclusive; per-decay-mode values from XSDB)
     • zz_gg: LO $\times k=1.7$ ($47.43$ fb inclusive; values symmetric by lepton universality from Torben's slides)
   • Updated zz_qqbar 13 TeV inclusive: XSDB LO $\times k=1.51$ (LO$\to$NNLO) $= 12.14 \times 1.51 = 18.3314$ pb

2. WZ Decay-Mode Cross Sections (processes/ewk.py):

   • All WZ decay-mode processes now have explicit 13.6 TeV cross sections using XSDB NLO values $\times k=1.08$ (NLO POWHEG $\to$ NNLO QCD $\times$ NLO EW from MATRIX):
     • wz_wlnu_zll (WZto3LNu): $4.924 \times 1.08 = 5.318$ pb (WZ Run3 paper)
     • wz_wqq_zll (WZto2L2Q): $7.568 \times 1.08 = 8.173$ pb (verified from CMS AN-2023/179)
     • wz_wlnu_zqq (WZtoLNu2Q): $15.87 \times 1.08 = 17.14$ pb (GenXSecAnalyzer verified)
     • wz_wqq_zqq (WZto4Q): $24.97 \times 1.08 = 26.97$ pb (GenXSecAnalyzer verified; XSDB mislabels this as "LO" but amcatnloFXFX is NLO — confirmed by 21% negative weight fraction)
   • 13 TeV wz_wlnu_zll: $4.430 \times 1.19 = 5.271$ pb (WZ Run2 paper)
   • 13 TeV values for other WZ decay modes still derived from inclusive via branching ratios
   • $k$-factor is between NNLO QCD $\times$ NLO EW (MATRIX) and NLO POWHEG (not NLO MATRIX) — both papers must be cited

3. New Process Definitions (processes/ewk.py):

   • wg_lnug: $W\gamma \to \ell\nu\gamma$ ($671.5 \pm 0.75$ pb at NLO from XSDB)
   • wpwp_jj: $W^\pm W^\pm jj$ same-sign WW ($0.0587 \pm 1.5\times 10^{-5}$ pb at LO from XSDB)

4. New Dataset Entries (Run 3 2024 Summer24 NanoAOD v15):

   • top.py: tttt_amcatnlo, ttg_amcatnlo, ttg_pt100to200_amcatnlo, ttg_pt200toinf_amcatnlo
   • higgs.py: thq_ctcvcp_madgraph, thw_ctcvcp_madgraph
   • ewk.py: wpwp_jj_ewkqcd_madgraph, wg_lnug_amcatnlo

Cross-Section References

Reference	Used for
PhysRevD 10.1103/2rr7-5xv3	ZZ inclusive NNLO+NNLL
MATRIX (arXiv:1912.00068)	WZ NNLO QCD $\times$ NLO EW
WZ Run3 (arXiv:2412.02477)	WZ $k=1.08$ (13.6 TeV)
WZ Run2 (arXiv:2110.11231)	WZ $k=1.19$ (13 TeV)
Torben's slides	ggZZ values
CMS AN-2023/179	WZto2L2Q verification