[bandlab] add extractor (supersedes #31206) (Closes #31184) #2993

Job	Run time
Linter	15s
Select tests from inputs	1s
Run tests (ubuntu-20.04, 2.7, cpython, core, sh)	1m 3s
Run tests (ubuntu-20.04, 3.2, cpython, core, sh)	1m 25s
Run tests (ubuntu-20.04, 3.5, cpython, core, sh)	1m 9s
Run tests (ubuntu-20.04, 3.9, cpython, core, sh)	1m 25s
Run tests (ubuntu-20.04, 3.11, cpython, core, sh)	57s
Run tests (ubuntu-20.04, pypy-2.7, cpython, core, sh)	2m 37s
Run tests (ubuntu-20.04, pypy-3.6, cpython, core, sh)	2m 59s
Run tests (ubuntu-20.04, pypy-3.7, cpython, core, sh)	3m 21s
Run tests (windows-2019, 3.4, cpython, core, bat)	2m 44s
Run tests (windows-2019, 3.4, cpython, nodownload, bat)	1m 52s
Run tests (ubuntu-20.04, 2.7, jython, core, sh)	3m 8s
Run tests (ubuntu-20.04, 2.7, jython, nodownload, sh)	25s
	23m 21s

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