CLI exits with status 1 after a successful run #2

copykat-py and copykat_matrix exit with status 1 after a successful run.

To reproduce (any input that completes normally):

copykat-py --input matrix.mtx --genes genes.tsv --barcodes barcodes.tsv \
    --sample-name s --output-dir out --no-plot-genes
echo $?   # prints 1

All output files are written correctly. The same happens with copykat_matrix; copykat-py-plot is not affected.

Why it matters: workflow managers and job schedulers (Snakemake, Nextflow, SLURM job dependencies, && chains in shell scripts) treat a non-zero exit status as a failure, so every successful run is reported as failed. run_copykat_py.sh passes the status through too.

Cause: main() and matrix_main() in copykat_py/cli.py return the result dict from _run_copykat_analysis(). The console scripts that pip/setuptools generate for [project.scripts] call sys.exit(main()), and sys.exit() given a non-integer exits with status 1 (after printing the value to stderr, which is the visible symptom: the result dict appears on the terminal at the end of every run).

Proposed fix: have the two entry points not return the result. Python callers who want the results already get them from copykat() and copykat_anndata(), which are unchanged. Fixed in #3: both commands then exit 0, a failing run (e.g. a missing input file) still exits 1, and all output files are byte-identical.