docs(codec): PR-X12 substrate canon resolutions — 18 open items resolved #457

Job	Run time
nostd/thumbv6m-none-eabi/stable	27s
clippy/1.95.0	45s
format/stable	23s
native-backend/stable	7m 50s
Pass MSRV values to other jobs	3s
tier4-avx512-check	32s
hpc-stream-parallel/rayon	1m 21s
docs/nightly	0s
miri	0s
nightly-simd-polyfill	0s
cargo-careful	0s
cross_test/${{ matrix.target }}/${{ matrix.rust }}	0s
tests/1.95.0	10m 52s
tests/beta	10m 53s
tests/stable	10m 51s
blas-msrv	52s
conclusion	0s
	44m 49s

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