Introduce package for Briefcase Automation #3692

Job	Run time
Check towncrier / Towncrier Checks	33s
Pre-commit checks / Pre-commit Checks	47s
Python package / Create Python Package	1m 12s
Unit tests (macos, 3.8)	2m 2s
Unit tests (macos, 3.9)	1m 45s
Unit tests (macos, 3.10)	2m 2s
Unit tests (macos, 3.11)	1m 44s
Unit tests (macos, 3.12)	2m 48s
Unit tests (ubuntu, 3.8)	1m 16s
Unit tests (ubuntu, 3.9)	1m 18s
Unit tests (ubuntu, 3.10)	1m 15s
Unit tests (ubuntu, 3.11)	1m 21s
Unit tests (ubuntu, 3.12)	1m 49s
Unit tests (windows, 3.8)	2m 15s
Unit tests (windows, 3.9)	2m 43s
Unit tests (windows, 3.10)	2m 4s
Unit tests (windows, 3.11)	2m 34s
Unit tests (windows, 3.12)	2m 51s
Project coverage	37s
Build app	0s
Verify project	0s
	32m 56s

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