Add two-photon continuum #142

Job	Run time
precommit / Load tox environments	6s
test / Load tox environments	4s
test / py311 (macos-latest)	15m 24s
test / py311 (windows-latest)	10m 22s
test / py39 (ubuntu-latest)	7m 5s
test / py310 (ubuntu-latest)	7m 7s
test / py311 (ubuntu-latest)	6m 59s
precommit / pre-commit (ubuntu-latest)	40s
docs / Load tox environments	6s
test_database_v9 / Load tox environments	6s
test_full_database / Load tox environments	6s
test_full_database / py311 (ubuntu-latest)	11m 22s
test_database_v9 / py311 (ubuntu-latest)	2m 56s
docs / build_docs (ubuntu-latest)	2m 22s
publish	0s
	1h 4m 45s

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