reduce low-level byte fiddling in openexr encoder #987

Job	Run time
Fuzz targets (afl)	1m 57s
build_benchmarks	1m 20s
cargo-deny	30s
Fuzz targets (cargo-fuzz)	6m 52s
clippy	3m 22s
public_private_dependencies	23s
rustfmt	17s
test_avif	1m 57s
test_avif_decoding	2m 0s
test_big_endian	1m 48s
test_big_endian (default)	4m 3s
test_features	51s
test_big_endian (webp)	1m 59s
verify_msrv	3m 12s
test_features (default)	1m 55s
test_toolchains (1.61.0)	3m 33s
test_big_endian (webp-encoder)	3m 21s
test_features (gif)	1m 11s
test_toolchains (nightly)	3m 12s
test_features (jpeg)	1m 1s
test_toolchains (beta)	2m 46s
test_features (png)	1m 5s
test_features (tiff)	1m 1s
test_features (ico)	1m 1s
test_features (pnm)	54s
test_features (tga)	52s
test_features (webp)	50s
test_features (bmp)	49s
test_features (hdr)	48s
test_features (dxt)	1m 2s
test_features (dds)	57s
test_features (farbfeld)	1m 1s
test_features (openexr)	1m 19s
test_features (jpeg_rayon)	1m 3s
test_features (webp-encoder)	1m 25s
	1h 1m 37s

Provide feedback