v2-docs: Switch to pydata-sphinx theme #1030

Job	Run time
build-vegafusion-python-osx-64	31m 0s
build-vegafusion-python-linux-64	15m 25s
build-vegafusion-python-linux-arm64	16m 17s
build-vegafusion-python-osx-arm64	22m 26s
build-vegafusion-python-win-64	42m 13s
build-vegafusion-server-linux-64	17m 2s
build-vegafusion-server-linux-arm64	14m 45s
build-vegafusion-server-osx-64	35m 13s
build-vegafusion-server-osx-arm64	19m 47s
build-vegafusion-server-win-64	41m 53s
build-vegafusion-wasm	12m 28s
check-rust	8m 25s
check-vegafusion-python	11m 15s
test-rust (ubuntu-20.04)	25m 57s
test-rust (windows-2022)	48m 13s
test-rust (macos-14)	29m 7s
test-vegafusion-python-linux-64	25m 23s
test-vegafusion-python-osx-arm64	1m 5s
test-vegafusion-python-win-64	1m 48s
	6h 59m 42s

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