MAINT: Integrate with custom feedstocks

[HaoZeke]

Not an immediate concern, but the recipes built within lab-cosmo, e.g. LAMMPS-Metatomic and the plumed-metatomic should be able to trigger a build of the cookbook recipes before being uploaded to the metatensor channel (or even the conda-forge one).

[Luthaf]

For more context, the idea is to test new builds before they are released, and catch any error early!

[ceriottm]

Idea is great, although TBH it's already pretty good to have the cookbook as an early warning system.