[task #14691] cosmiccal: handle stdin and act as a filter to stdout

[Boud Roukema]

Follow-up Comment #1, task#14691 (group gnuastro):

Commit 7fc6dc81 on branch cosmo_benchmark [1] shows the slowdown induced by
requiring the input parameter to be a command line option rather than be read
from stdin. LSST/Rubin [2] will give us billions of galaxies with photo-z's -
at 1 microsecond/redshift. With 1 cpu, a billion redshifts will take 1000
seconds to convert to comoving radial distances with 'cosmdist' 0.3.12, or 50
million seconds (about a year and a half) with 'cosmiccal'.

For a further speedup, see https://savannah.gnu.org/bugs/index.php?65195 for
the flat case.


tests$ ./cosmiccal/benchmark.sh

astcosmiccal, N_big1=1000:
real    0m18.769s
user    0m14.561s
sys     0m6.386s

cosmdist, N_big1=1000:
real    0m0.128s
user    0m0.129s
sys     0m0.000s

cosmdist, N_big2=1000000:
real    0m0.945s
user    0m0.932s
sys     0m0.034s

cosmdist, N_big3=10000000:
real    0m8.272s
user    0m8.244s
sys     0m0.232s


Caveats for this back-of-the-envelope benchmarking:
* I didn't continue 'cosmiccal' to the full extent of proportionality to N,
but I think it's close enough;
* the results from 1M to 10M for 'cosmdist' seem close enough to
proportionality to N for a back-of-the-envelope estimate.

[1]
https://codeberg.org/boud/gnuastro/commit/7fc6dc81bb30c573d0d4b08320c3dd9d4c54eac2

[2] https://community.lsst.org


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