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feature: shadow mapping, directional and spot lights #508

Job	Run time
renderling-test-linux	4m 14s
renderling-build-example	2m 33s
renderling-test-macos	1m 53s
renderling-test-windows	1m 58s
install-cargo-gpu (ubuntu-latest)	1m 28s
install-cargo-gpu (macos-latest)	1m 19s
install-cargo-gpu (windows-latest)	2m 19s
renderling-clippy	1m 51s
renderling-build-shaders (ubuntu-latest)	49s
renderling-build-shaders (macos-latest)	46s
renderling-build-shaders (windows-latest)	38s
	19m 48s

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