remove regress_stress/forces and direct_forces properties

[lbluque]

Summary

• Removed redundant property wrappers (direct_forces, regress_forces, regress_stress) from HydraInterfaceMixin, eSCNMDBackbone, MLP_EFS_Head, DatasetSpecificMoEWrapper, and DatasetSpecificSingleHeadWrapper that simply delegated to regress_config
• Updated all call sites to access regress_config directly (e.g., self.regress_config.direct_forces instead of self.direct_forces)
• In HydraInterfaceMixin.skip_property, replaced self.direct_forces with a safe getattr lookup on backbone.regress_config to avoid assuming all backbones have this attribute
• Removed the direct_forces property from MLIPPredictUnit and inlined the access through self.model.module.backbone.regress_config.direct_forces
• Removed the now-irrelevant test_direct_forces_property test

[wood-b]

lgtm, but its a but hard to track what flags get set in the model config? and has this been tested across all scenarios we care about e.g. conservative forces, direct forces, direct stress, etc?