Add two-photon continuum #161

Job	Run time
precommit / Load tox environments	8s
test / Load tox environments	6s
test / py311 (macos-latest)	8m 36s
test / py311 (windows-latest)	10m 31s
test / py39 (ubuntu-latest)	7m 16s
test / py310 (ubuntu-latest)	7m 18s
test / py311 (ubuntu-latest)	7m 13s
precommit / pre-commit (ubuntu-latest)	35s
docs / Load tox environments	7s
test_database_v9 / Load tox environments	6s
test_full_database / Load tox environments	4s
test_full_database / py311 (ubuntu-latest)	10m 36s
test_database_v9 / py311 (ubuntu-latest)	2m 49s
docs / build_docs (ubuntu-latest)	6m 41s
publish	0s
	1h 2m 6s

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