Relation operations

Relation operations expose the same relation builders used internally by convolution, pooling, and neighbor queries. They are useful when an application needs to inspect sparse connectivity, reuse relation metadata, or gather neighbor features explicitly.

Kernel relations are lattice relations over integer coordinates. Neighbor relations are geometric query/source relations over sparse rows and carry distances in edge order.

Submanifold relations are explicit relation objects. They fix output support to the input coordinate identity while still exposing the same edge arrays, CSR views, and implicit-GEMM views as compatible forward relations. This keeps subm_conv3d semantically distinct from generic forward convolution without duplicating backend kernels.