fix(cuda): correct revolute joint axis direction for right-handed rotation

[Ligo04]

Summary

• Fix revolute joint axis direction (UnitE) by reversing it from (P0 - P1) to (P1 - P0), ensuring positive angles follow right-handed spiral rotation around the joint axis.
• Applied consistently in both the joint constitution and external force constraint.

[gemini-code-assist]

Summary of Changes

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This pull request resolves an issue in the CUDA backend where the revolute joint axis direction was incorrectly defined. By reversing the vector subtraction used to calculate the UnitE vector, the system now accurately adheres to the right-handed rotation convention. This correction ensures that joint movements and external force constraints are simulated with the proper directional orientation, improving the overall physical accuracy of the simulation.

Highlights

• Revolute Joint Axis Direction: Reversed the calculation of the revolute joint axis direction (UnitE) from (P0 - P1) to (P1 - P0) to ensure positive angles follow a right-handed spiral rotation.
• Consistency Across Implementations: Applied the corrected axis direction consistently in both the joint constitution and the external force constraint implementations for revolute joints.

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[gemini-code-assist]

Code Review

This pull request modifies the calculation of the UnitE vector in two files related to affine body revolute joints: affine_body_revolute_joint.cu and affine_body_revolute_joint_external_force_constraint.cu. The change reverses the order of subtraction from (P0 - P1) to (P1 - P0) when determining UnitE, likely correcting the vector's direction for physical accuracy. There are no review comments to address.