Resolve "Fix GPU version of mesh_batch_dotp_matrix for spinors and add unit tests"

Description

Add GPU support for dotp_matrix for spinors and also extend the unit test for the routine to test spinors.

News snippet

Add GPU support for dotp_matrix for spinors.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.

Closes #307 (closed) #310 (closed)