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feature: shadow mapping, directional and spot lights #507

Job	Run time
renderling-build-example	2m 17s
renderling-test-linux	3m 55s
renderling-clippy	1m 40s
install-cargo-gpu (ubuntu-latest)	1m 20s
install-cargo-gpu (macos-latest)	1m 5s
renderling-test-macos	4m 10s
renderling-test-windows	4m 5s
install-cargo-gpu (windows-latest)	2m 47s
renderling-build-shaders (ubuntu-latest)	45s
renderling-build-shaders (macos-latest)	39s
renderling-build-shaders (windows-latest)	28s
	23m 11s

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