Update GEMM (#424)

* Organize and collect metal subroutine templates and elements in `metal/kernels/steel/`
* Update gemm elements for better performance 
* Add split-K specialization for gemm
* Add `addmm` primitive, op and bindings for fused matmul and bias addition 
* Update tests and benchmarks as needed

python/src/ops.cpp

@@ -3476,4 +3476,34 @@ void init_ops(py::module_& m) {
       Returns:
         result (array): The tiled array.
     )pbdoc");
+  m.def(
+      "addmm",
+      &addmm,
+      "c"_a,
+      "a"_a,
+      "b"_a,
+      py::pos_only(),
+      "alpha"_a = 1.0f,
+      "beta"_a = 1.0f,
+      py::kw_only(),
+      "stream"_a = none,
+      R"pbdoc(
+        addmm(c: array, a: array, b: array, /, alpha: float = 1.0, beta: float = 1.0,  *, stream: Union[None, Stream, Device] = None) -> array
+
+        Matrix multiplication with addition and optional scaling.
+
+        Perform the (possibly batched) matrix multiplication of two arrays and add to the result
+        with optional scaling factors.
+
+        Args:
+            c (array): Input array or scalar.
+            a (array): Input array or scalar.
+            b (array): Input array or scalar.
+            alpha (float, optional): Scaling factor for the 
+                matrix product of ``a`` and ``b`` (default: ``1``)
+            beta (float, optional): Scaling factor for ``c`` (default: ``1``)
+
+        Returns:
+            array: ``alpha * (a @ b)  + beta * c``
+      )pbdoc");
 }