add mammoth and cobble to conda

[purpleelephant123]

Hi, I am wondering if I might be able to add mammoth and cobble to conda-forge? Note, it would probably be easier to maintain if you were to do it. But I'll just do it anyway if I don't hear back from you. No worries either way.

[mwilliamson]

I don't really know anything about conda-forge beyond the superficial so I'm unlikely to add any packages, and have no strong opinions on others doing so.

[sarthakpati]

I am working on these:

• cobble: added recipe for cobble conda-forge/staged-recipes#28581
• mammoth: added recipe for mammoth conda-forge/staged-recipes#28583