chore: bump version to v0.2.1 (#18) #4

Job	Run time
build / check / check	23m 23s
build / Build (aarch64-apple-darwin)	29m 24s
build / Build (x86_64-unknown-linux-gnu)	27m 20s
build / Build sdist	13m 53s
build / Build (aarch64-unknown-linux-gnu)	20m 56s
build / Build (x86_64-apple-darwin)	24m 43s
Publish to PyPI	51s
	2h 20m 30s

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