Add PCX decoder support #1651

Job	Run time
test_avif_decoding	1m 27s
test_toolchains (1.70.0)	29s
test_toolchains (nightly)	1m 4s
Fuzz targets (afl)	2m 5s
build_benchmarks	47s
test_toolchains (beta)	1m 21s
Fuzz targets (cargo-fuzz)	53s
cargo-deny	21s
cargo-semver-checks	27s
clippy	2m 3s
public_private_dependencies	25s
rustfmt	12s
test_features	27s
test_other_archs (powerpc-unknown-linux-gnu)	2m 26s
test_features (default)	1m 49s
test_other_archs (i686-unknown-linux-gnu)	1m 46s
test_features (rayon)	25s
test_features (avif)	1m 0s
test_features (bmp)	26s
test_features (dds)	25s
test_features (exr)	40s
test_features (ff)	28s
test_features (gif)	25s
test_features (hdr)	22s
test_features (ico)	41s
test_features (jpeg)	24s
test_features (png)	37s
test_features (pnm)	24s
test_features (qoi)	22s
test_features (tga)	29s
test_features (tiff)	37s
test_features (webp)	27s
	26m 14s

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