fix: mark package as side-effect free #331

Job	Run time
check	57s
test-chrome-webworker	26s
test-firefox	24s
test-firefox-webworker	21s
test-chrome	29s
test-node (windows-latest, lts/*)	2m 20s
test-node (ubuntu-latest, lts/*)	37s
test-electron-main	28s
test-node (macos-latest, lts/*)	1m 54s
test-webkit (ubuntu-latest, lts/*)	9s
test-electron-renderer	20s
test-webkit (macos-latest, lts/*)	1m 24s
test-webkit-webworker (ubuntu-latest, lts/*)	10s
test-webkit-webworker (macos-latest, lts/*)	1m 39s
release	0s
	11m 38s

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