Refactor `eprop_iaf_psc_delta` models #326

Job	Run time
clang-format	22s
cppcheck	6m 56s
rstcheck	24s
copyright_headers	21s
isort	16s
forbidden_types	20s
lychee_IGNORED	27s
mypy	36s
pydocstyle	21s
pylint	40s
unused_names	17s
black	32s
flake8	26s
vale	33s
build_linux (ubuntu-22.04, gcc, boost, optimize, warning)	14m 14s
build_macos (macos-latest, clang, openmp, mpi, python, gsl, ltdl, boost, hdf5, optimize, warning)	15m 54s
build_linux (ubuntu-22.04, gcc, openmp, python, gsl, ltdl, boost, optimize, warning)	19m 52s
build_linux (ubuntu-22.04, gcc, mpi, python, gsl, ltdl, boost, optimize, warning)	21m 15s
build_linux (ubuntu-22.04, gcc, openmp, mpi, python, gsl, ltdl, boost, hdf5, sionlib, libneurosim...	31m 32s
sphinx-rtd	3m 41s
sphinx-conda	0s
	1h 58m 59s

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