ldpc: Add version 2.4.1 - #4770

bp_decoder's Cython extension compiles and packages into the wheel fine
(confirmed from the full build log: _bp_decoder.cpython-313-riscv64-linux-gnu.so
is built and added, same as union_find_decoder's). The CI failure is purely in
our own CIBW_TEST_COMMAND sanity check.

ldpc/__init__.py's "Legacy syntax" section does
`from ldpc.bp_decoder import bp_decoder`, which rebinds the `ldpc` package's
own `bp_decoder` attribute (set by the import machinery to the submodule
object) to the legacy `bp_decoder` callable that
ldpc/bp_decoder/__init__.py also exports under that same name. After
`import ldpc` runs, `ldpc.bp_decoder` is that callable, not the submodule, so
a later `ldpc.bp_decoder._bp_decoder` attribute access raises
"ImportError: cannot import name '_bp_decoder' from 'bp_decoder' (unknown
location)" on any install, on any architecture -- reproduced locally with a
minimal stand-in package. union_find_decoder has no such legacy-name
collision, which is why it alone appeared to "work" in the same test command.

Resolve the compiled submodule by name with importlib.import_module instead,
which looks it up in sys.modules directly and is unaffected by the shadowed
attribute.

build-ldpc.yml's setup job excludes cp39/cp310/cp311 from the build
matrix (stim and pymatching, both hard runtime dependencies, ship no
riscv64 wheel below cp312), but docs/packages/ldpc.yaml still listed
3.10:manylinux and 3.11:manylinux as files the release must contain.
That made ci_scripts/update_doc.py's release-completeness check fail
on every run with "release is incomplete; no wheel was built for:
3.10:manylinux, 3.11:manylinux", since those targets can never be
built. Match the files list to the matrix actually built, same as
cyhunspell's docs/packages/cyhunspell.yaml does for its own exclusions.

_publish-wheel.yml now requires a matrix input (main's "publish:
Validate effective wheel targets"), but this PR branch forked before
that landed and ldpc has never been merged to main, so build-ldpc.yml
never picked up the matching one-line update every already-published
package's workflow got. The merge ref combines the new required-input
_publish-wheel.yml with this branch's old build-ldpc.yml, so every run
has failed startup with "Input matrix is required, but not provided".

Pass it the same way the mass-update commit did for every other
package's publish job.