Add PCX decoder support #1654

Job	Run time
test_features	27s
build_benchmarks	47s
test_features (default)	1m 52s
Fuzz targets (afl)	2m 10s
Fuzz targets (cargo-fuzz)	53s
test_features (rayon)	25s
test_features (avif)	58s
cargo-deny	18s
test_features (bmp)	23s
cargo-semver-checks	1m 7s
clippy	2m 1s
test_features (dds)	23s
test_features (exr)	44s
public_private_dependencies	24s
rustfmt	12s
test_features (ff)	28s
test_avif_decoding	1m 23s
test_features (gif)	29s
test_toolchains (1.70.0)	32s
test_features (hdr)	23s
test_other_archs (powerpc-unknown-linux-gnu)	2m 25s
test_toolchains (nightly)	1m 10s
test_features (ico)	29s
test_other_archs (i686-unknown-linux-gnu)	1m 27s
test_toolchains (beta)	1m 17s
test_features (jpeg)	23s
test_features (pcx)	16s
test_features (png)	36s
test_features (pnm)	28s
test_features (qoi)	29s
test_features (tga)	24s
test_features (tiff)	33s
test_features (webp)	28s
	26m 44s

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