Fixes the body index used for computing end-effector Jacobian

[Mayankm96]

Description

The Jacobians returned from ArticulationView follow the shape: [batch, body, 6, dof]. However, it does not include the base body. For Franka Panda arm, this means:

jacob:  torch.Size([128, 10, 6, 9])
bodies:  ['panda_link0', 'panda_link1', 'panda_link2', 'panda_link3', 'panda_link4', 'panda_link5', 'panda_link6', 'panda_link7', 'panda_hand', 'panda_leftfinger', 'panda_rightfinger']
num_bodies:  11
num_dof: 9

Thus, we need to account for the base link when retrieving the Jacobian:

self._data.ee_jacobian[:] = jacobians[:, self.ee_body_index - 1, :,  : self.arm_num_dof]

Fixes #21

Type of change

• Bug fix (non-breaking change which fixes an issue)

Screenshots

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Checklist

• I have run the pre-commit checks with pre-commit run --all-files (see here instructions to set it up)
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have updated the changelog and the corresponding version in the extension's config/extension.toml file