Adds Databricks backend #822

Job	Run time
Build Docs	1m 55s
Test a fork PR (no secrets)	0s
Test Posit Connect	1m 46s
Tests (3.9, ubuntu-latest, --workers 4 --tests-per-worker 1)	59s
Tests (3.10, ubuntu-latest, --workers 4 --tests-per-worker 1)	51s
Tests (3.11, ubuntu-latest, --workers 4 --tests-per-worker 1)	50s
Tests (3.12, ubuntu-latest, --workers 4 --tests-per-worker 1)	1m 1s
Tests (3.13, ubuntu-latest, --workers 4 --tests-per-worker 1)	1m 0s
Tests (ubuntu-latest, 3.9, requirements/minimum.txt)	54s
Tests (macos-latest, 3.10, --workers 4 --tests-per-worker 1 -k pins/tests)	56s
Tests (windows-latest, 3.10, -k pins/tests)	5m 22s
Preview Docs:	34s
Publish Docs	0s
Release to pypi	0s
	16m 8s

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