The CSR hierarchy should implement sparse tensors (N-D) with CSR format. This should follow the same pattern as xmap_container classes:

• xcsr_container is a CRTP base class that gathers common implementation and API of inheriting classes
• xcsr_array inherits from xcsr_container and implements the case where the number of dimensions is dynamic
• xcsr_tensor inherits from xcsr_container and implements the case where the number of dimensions is static