Include user sensor dimensions in model signature

[rajatmohan22]

Summary

Fixes #3307.

mjCModel::Signature() currently includes each sensor's type, but not its dimension. For mjSENS_USER, the sensor dim directly affects nsensordata and therefore the compiled model memory layout. This meant two models with different user sensor dimensions could incorrectly share the same model signature.

This PR includes sensor dim in the model signature and adds a regression test for user sensors with different dimensions.

Changes

• Include sensor.spec.dim when hashing sensors in mjCModel::Signature().
• Add a regression test verifying that two mjSENS_USER sensors with different dimensions produce different model signatures.

Test

./build-appleld/bin/user_objects_test --gtest_filter=SensorTest.UserSensorDimAffectsModelSignature

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.