feat: add default screenshot format configuration and update readme.md docs #1533

Job	Run time
Tests on ubuntu-latest with node 22	35s
Tests on windows-latest with node 24	1m 9s
Tests on ubuntu-latest with node 20	34s
Tests on ubuntu-latest with node 23	33s
Tests on windows-latest with node 22	1m 24s
Tests on windows-latest with node 23	1m 10s
Tests on windows-latest with node 20	1m 12s
Tests on macos-latest with node 22	48s
Tests on macos-latest with node 20	55s
Tests on macos-latest with node 23	40s
Tests on macos-latest with node 24	43s
Tests on ubuntu-latest with node 24	39s
[Required] Tests passed	2s
	10m 24s

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