metal : mark FA blocks (#16372)

* metal : better unroll in the FA kernels

* metal : index FA blocks

* tests : restore [no ci]

* metal : prevent division by zero in FA kernels

* metal : fix -INF detection logic

ggml/src/ggml-metal/ggml-metal-ops.h

@@ -40,6 +40,7 @@ size_t ggml_metal_op_mul_mat_id_extra_ids(const struct ggml_tensor * op);
 bool ggml_metal_op_flash_attn_ext_use_vec(const struct ggml_tensor * op);
 
 size_t ggml_metal_op_flash_attn_ext_extra_pad(const struct ggml_tensor * op);
+size_t ggml_metal_op_flash_attn_ext_extra_blk(const struct ggml_tensor * op);
 size_t ggml_metal_op_flash_attn_ext_extra_tmp(const struct ggml_tensor * op);
 
 int ggml_metal_op_concat            (ggml_metal_op_t ctx, int idx);