Fix for subjob spawning with FIFOs

[jackal1-66]

When running jobs spawning with GeneratorFileOrCmd it could happen that the subjob is still running after the FIFO has been deleted by the destructor. This was not a problem before the destructors Fix, but it is now, especially in situations in which the number of events to be generated by the subgenerator exceeds the actual needed number for the o2-sim generation (such as hyperloop configurations). This fix implements a different spawning mechanism using fork() and allows the destructor to kill the subjobs via their PIDs.

[github-actions]

REQUEST FOR PRODUCTION RELEASES:
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The following labels are available
async-2023-pbpb-apass4
async-2023-pp-apass4
async-2024-pp-apass1
async-2022-pp-apass7
async-2024-pp-cpass0
async-2024-PbPb-apass1
async-2024-ppRef-apass1

[alibuild]

Error while checking build/O2/fullCI for 18899fe at 2024-12-20 03:56:

## sw/BUILD/O2-latest/log
c++: error: unrecognized command-line option '--rtlib=compiler-rt'
c++: error: unrecognized command-line option '--rtlib=compiler-rt'


## sw/BUILD/o2checkcode-latest/log
--
========== List of errors found ==========
++ GRERR=0
++ grep -v clang-diagnostic-error error-log.txt
++ grep ' error:'
/sw/SOURCES/O2/13824-slc8_x86-64/0/Generators/src/GeneratorFileOrCmd.cxx:20:10: error: inclusion of deprecated C++ header 'signal.h'; consider using 'csignal' instead [modernize-deprecated-headers]
++ [[ 0 == 0 ]]
++ exit 1
--

Full log here.