Madgraph + Pythia with ISR

### Check duplicate issues.

- [x] Checked for duplicates

### Goal

Running MG + Pythia without ISR is ok, but of ISR is turned on:
- accepted/trials is not 100%
- error message is "cannot set mass"
- severity increases with sqrts
- leads to a modification of the cross section by a factor acc/trials
- can lead to abort

Issue opened with Pythia: [https://gitlab.com/Pythia8/releases/-/issues/564](https://gitlab.com/Pythia8/releases/-/issues/564)

### Operating System and Version

all

### compiler

all

### The version of the key4hep stack

all

### Package Version

all

### Reproducer

k4GeneratorsConfig ../examples/FermionProduction.yaml
cd Run-Cards/Madgraph/Muon350
./Run_Muon350_ISR.dat

### Additional context

_No response_

Start by running k4GeneratorsConfig ../examples/FermionProduction.yaml, then inspect Run-Cards/Madgraph/Muon350/Run_Muon350_ISR.dat and reproduce the ISR failure. Compare the run with ISR disabled and review the linked Pythia issue for context. Done means no "cannot set mass" errors or aborts, accepted/trials is not reduced, and the cross section is not distorted.

Written by the indexing model from the issue text.