nx_gguf_load_block_test.nx

nx_gguf_load_block_test.nx -- smoke for nx_gguf_load_block.nx. Two test classes: A) Name-formatting unit checks: format "blk.{N}.{suffix}" with different layer indices + suffix strings; verify byte-equal to expected literal. B) End-to-end integration: build a synthetic GGUF with a single layer-0 attn_norm tensor (F32 shape [2]); call the loader's _gbl_load_blk_tensor; verify it finds + loads correctly. Full 9-tensor end-to-end smoke is deferred to the `nx_llm_run` v2 brick where it composes with the transformer block forward pass. THIS smoke validates the new code paths (name fmt + per-tensor helper) under the bits-up canonical-brick discipline.