Add PCX decoder support #1657

Job	Run time
Fuzz targets (afl)	2m 15s
cargo-deny	18s
build_benchmarks	46s
Fuzz targets (cargo-fuzz)	52s
cargo-semver-checks	36s
clippy	2m 12s
public_private_dependencies	22s
rustfmt	12s
test_avif_decoding	1m 22s
test_features	22s
test_other_archs (powerpc-unknown-linux-gnu)	2m 34s
test_toolchains (1.70.0)	35s
test_features (default)	1m 52s
test_other_archs (i686-unknown-linux-gnu)	1m 43s
test_toolchains (nightly)	1m 11s
test_features (rayon)	31s
test_toolchains (beta)	1m 32s
test_features (avif)	1m 0s
test_features (bmp)	34s
test_features (dds)	32s
test_features (exr)	56s
test_features (ff)	21s
test_features (gif)	29s
test_features (hdr)	24s
test_features (ico)	47s
test_features (jpeg)	30s
test_features (pcx)	23s
test_features (png)	27s
test_features (pnm)	28s
test_features (qoi)	31s
test_features (tga)	22s
test_features (tiff)	31s
test_features (webp)	26s
	27m 56s

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