Orbv3 Updates

[AdeeshKolluru]

Summary

Adapts the OrbModel with recent changes in OrbCalculator and updates tests with both direct and conservative OrbV3 models.

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[orionarcher]

LGTM! one comment

[CompRhys]

LGTM

One nit - I think that the code about "direct_stress" and "direct_forces" might be better to remove because it doesn't get triggered for the v3 models?

[orionarcher]

Good to merge? I am going to mint a v0.2 release soon and this would be nice to include.