DOC: use `invariants` and `masses` attributes #302

Job	Run time
pytest / Determine job matrix	7s
style / Determine skipped pre-commit hooks	10s
doc / nb / Execute and build documentation	5m 35s
doc / linkcheck / Check external links	52s
pytest / Run unit tests (3.10, ubuntu-22.04)	27s
pytest / Run unit tests (3.11, ubuntu-22.04)	26s
pytest / Run unit tests (3.12, ubuntu-22.04)	24s
pytest / Run unit tests (3.8, ubuntu-22.04)	21s
pytest / Run unit tests (3.9, ubuntu-22.04, ampform_dpd)	27s
pytest / Run unit tests (3.9, macos-12)	1m 47s
style / Run taplo through pre-commit	21s
style / Run local pre-commit hooks	1m 25s
style / Push changes	0s
doc / Upload to GitHub Pages	0s
	12m 22s

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