Dict-like methods of `Dataset`. #450

Job	Run time
Formatting and static analysis	1m 3s
Tests ubuntu-22.04 pydantic1-full	2m 37s
Tests ubuntu-22.04 py311-full	3m 17s
Tests ubuntu-22.04 py311-full	2m 36s
Tests ubuntu-22.04 py310-full	2m 39s
Tests ubuntu-22.04 py39-full	2m 54s
Tests ubuntu-22.04 py38-full	2m 41s
Tests macos-12 py38	2m 29s
Tests windows-2022 py38	2m 45s
docs / Build documentation	2m 32s
	25m 33s

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