add optional torchgeo and torch dependencies, their platform requirem…

[rbavery]

Description

this adds optional dependencies for torch, torchvision, pytorch-triton, and torchgeo. It pins torchgeo and torch to recent prereleases so that we can test and be ready for upcoming torch 2.8 pt2 export and load apis.

Once torch 2.8 is released, we can then pin torch and torchgeo to stable versions in stac-model and make a new release of stac-model to allow for saving and loading pt2 archives with automatically filled in metadata stored in yaml

Related Issue

torchgeo/torchgeo#2880

Type of Change

• 📚 Examples, docs, tutorials or dependencies update;
• 🔧 Bug fix (non-breaking change which fixes an issue);
• 🥂 Improvement (non-breaking change which improves an existing feature);
• 🚀 New feature (non-breaking change which adds functionality);
• 💥 Breaking change (fix or feature that would cause existing functionality to change);
• 🔐 Security fix.

Checklist

• I've read the CONTRIBUTING.md guide;
• I've updated the code style using make check;
• I've written tests for all new methods and classes that I created;
• I've written the docstring in Google format for all the methods and classes that I used.