Add AVIF plugin (decoder + encoder using libavif) #551

Job	Run time
Windows x86	19m 32s
Windows AMD64	17m 49s
Windows ARM64	12m 9s
macOS 10.10 x86_64	41m 33s
macOS 10.13 x86_64	45m 0s
macOS 10.15 x86_64	37m 21s
macOS arm64	28m 10s
sdist	22s
manylinux2014 and musllinux x86_64	1h 25m 1s
manylinux_2_28 x86_64	38m 54s
manylinux2014 and musllinux aarch64	1h 3m 36s
manylinux_2_28 aarch64	32m 22s
Upload wheels to scientific-python-nightly-wheels	0s
Upload release to PyPI	0s
	7h 1m 49s

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