feat(codec): PR-X12 A2 mode bit-pack + A3-intra prediction kernel #446

Job	Run time
tier4-avx512-check	30s
Pass MSRV values to other jobs	3s
hpc-stream-parallel/rayon	1m 21s
clippy/1.95.0	40s
format/stable	21s
native-backend/stable	7m 55s
nostd/thumbv6m-none-eabi/stable	25s
cross_test/${{ matrix.target }}/${{ matrix.rust }}	0s
docs/nightly	0s
miri	0s
cargo-careful	0s
nightly-simd-polyfill	0s
blas-msrv	1m 7s
tests/stable	10m 52s
tests/beta	11m 19s
tests/1.95.0	11m 25s
conclusion	-1s
	45m 57s

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