Add gcta/makebksparse module

[lyh970817]

This PR adds the gcta/makebksparse module, which creates a sparse GRM for downstream fastGWA analyses.

This PR should merge after the gcta/makegrm module in #11650.

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• nf-core modules test gcta/makebksparse --profile docker
• nf-core modules test gcta/makebksparse --profile singularity
• nf-core modules test gcta/makebksparse --profile conda

[lyh970817]

Rationale for the meta rebinding at modules/nf-core/gcta/makebksparse/main.nf:L24:

The input meta.id identifies the dense GRM basename required by gcta --grm. makebksparse emits a new sparse GRM basename via --out ${prefix}_sp, and downstream consumers use that basename with --grm-sparse. Rebinding meta with meta + [id: "${prefix}_sp"] preserves any existing metadata while making the output tuple describe the emitted sparse GRM files rather than the dense input GRM.

The original dense basename is saved first as dense_prefix, so the command still consumes the dense GRM via --grm ${dense_prefix} while the emitted sparse_grm_files channel carries the sparse basename expected by downstream modules.