Add gnpy/api from 2021-candi branch to API-develop #218

Job	Run time
Tests on paywalled platforms (macos-13-xlarge, 3.12)	29s
Tox test (py38)	59s
Tests on other platforms (windows-2019, 3.10)	1m 42s
Tox test (py39)	58s
Tests on other platforms (windows-2022, 3.11)	1m 35s
Tox test (py310)	56s
Tox test (py311)	1m 0s
Tests on other platforms (windows-2022, 3.12)	1m 19s
Tox test (py312-cover)	1m 31s
Tests on other platforms (macos-12, 3.11)	1m 14s
Tox test (docs, graphviz)	1m 48s
Tests on other platforms (macos-13, 3.12)	54s
Docker image	0s
PyPI packaging	0s
	14m 25s

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