feat(codec): PR-X12 A2 mode bit-pack + A3-intra prediction kernel #448

Job	Run time
hpc-stream-parallel/rayon	1m 26s
tier4-avx512-check	31s
format/stable	21s
Pass MSRV values to other jobs	4s
nostd/thumbv6m-none-eabi/stable	25s
clippy/1.95.0	41s
native-backend/stable	7m 51s
docs/nightly	0s
nightly-simd-polyfill	0s
miri	0s
cross_test/${{ matrix.target }}/${{ matrix.rust }}	0s
cargo-careful	0s
tests/stable	11m 6s
tests/beta	9m 57s
tests/1.95.0	11m 11s
blas-msrv	52s
conclusion	-1s
	44m 24s

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