feat: separate span power from tx power #322

Job	Run time
Tox test (py38)	2m 34s
Tests on other platforms (windows-2019, 3.10)	3m 44s
Tests on paywalled platforms	0s
Tox test (py39)	2m 35s
Tests on other platforms (windows-2022, 3.11)	3m 17s
Tox test (py310)	2m 36s
Tests on other platforms (windows-2022, 3.12)	3m 18s
Tox test (py311)	2m 32s
Tests on other platforms (macos-12, 3.11)	2m 24s
Tox test (py312-cover)	5m 9s
Tests on other platforms (macos-13, 3.12)	2m 42s
Tox test (docs, graphviz)	1m 58s
PyPI packaging	0s
Docker image	0s
	32m 49s

Provide feedback