Add locking to prevent the dreaded concurrency bug and a download opt… #155

Job	Run time
pre-commit	10s
combine-environments	8s
unit-tests (3.11)	26s
integration-tests (3.11, -integration)	19s
docs-build	25s
type-check	26s
distribution	0s
upload-to-pypi	0s
	1m 54s

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