Add PCX decoder support #1650

Job	Run time
build_benchmarks	46s
cargo-deny	24s
Fuzz targets (afl)	2m 13s
Fuzz targets (cargo-fuzz)	1m 8s
cargo-semver-checks	31s
clippy	2m 4s
public_private_dependencies	26s
rustfmt	14s
test_avif_decoding	1m 23s
test_features	35s
test_other_archs (powerpc-unknown-linux-gnu)	2m 55s
test_features (default)	1m 56s
test_toolchains (1.70.0)	42s
test_other_archs (i686-unknown-linux-gnu)	1m 52s
test_features (rayon)	29s
test_toolchains (nightly)	1m 43s
test_features (avif)	1m 2s
test_toolchains (beta)	1m 55s
test_features (bmp)	35s
test_features (dds)	35s
test_features (exr)	47s
test_features (ff)	45s
test_features (gif)	41s
test_features (hdr)	42s
test_features (ico)	44s
test_features (jpeg)	40s
test_features (png)	35s
test_features (pnm)	24s
test_features (qoi)	21s
test_features (tga)	25s
test_features (tiff)	35s
test_features (webp)	31s
	30m 38s

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