Add PCX decoder support #1653

Job	Run time
Fuzz targets (afl)	2m 14s
cargo-deny	18s
build_benchmarks	46s
Fuzz targets (cargo-fuzz)	50s
cargo-semver-checks	29s
clippy	2m 11s
public_private_dependencies	26s
rustfmt	11s
test_avif_decoding	1m 24s
test_other_archs (powerpc-unknown-linux-gnu)	2m 38s
test_toolchains (1.70.0)	29s
test_other_archs (i686-unknown-linux-gnu)	1m 29s
test_toolchains (nightly)	1m 46s
test_features	33s
test_toolchains (beta)	1m 23s
test_features (default)	1m 49s
test_features (rayon)	37s
test_features (avif)	56s
test_features (bmp)	26s
test_features (dds)	27s
test_features (exr)	32s
test_features (ff)	24s
test_features (gif)	26s
test_features (hdr)	25s
test_features (ico)	37s
test_features (jpeg)	20s
test_features (png)	30s
test_features (pnm)	24s
test_features (qoi)	27s
test_features (tga)	30s
test_features (tiff)	30s
test_features (webp)	39s
	27m 6s

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