Add VERSIONING.md, ROADMAP.md, and DEPENDENCY_POLICY.md #4181

Job	Run time
checks / readme-snippets	15s
checks / pre-commit	33s
checks / test (3.10, highest, ubuntu-latest)	49s
checks / test (3.11, lowest-direct, ubuntu-latest)	46s
checks / test (3.12, highest, ubuntu-latest)	57s
checks / test (3.13, lowest-direct, windows-latest)	2m 28s
checks / test (3.13, lowest-direct, ubuntu-latest)	44s
checks / test (3.10, lowest-direct, ubuntu-latest)	45s
checks / test (3.13, highest, windows-latest)	3m 33s
checks / test (3.12, lowest-direct, ubuntu-latest)	50s
checks / test (3.12, lowest-direct, windows-latest)	3m 7s
checks / test (3.12, highest, windows-latest)	3m 26s
checks / test (3.10, highest, windows-latest)	2m 20s
checks / test (3.10, lowest-direct, windows-latest)	2m 21s
checks / test (3.11, highest, ubuntu-latest)	45s
checks / test (3.13, highest, ubuntu-latest)	46s
checks / test (3.11, lowest-direct, windows-latest)	2m 19s
checks / test (3.11, highest, windows-latest)	2m 28s
all-green	16s
	29m 28s

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