Add unit tests for the SIMD __rfloordiv__() method

The support for __rfloordiv__() with SIMD types was added in the following commit:
f5aee40

This commit includes:
  - Unit tests for __rfloordiv__() in SIMD types.
  - The missing constraint added to the method's implementation.

stdlib/src/builtin/simd.mojo

@@ -671,6 +671,7 @@ struct SIMD[type: DType, size: Int = simdwidthof[type]()](
         Returns:
             `floor(rhs / self)` value.
         """
+        constrained[type.is_numeric(), "the type must be numeric"]()
         return rhs // self
 
     @always_inline("nodebug")

stdlib/test/builtin/test_simd.mojo

@@ -222,6 +222,24 @@ def test_floordiv():
     assert_equal(Float32(2) // Float32(-2), -1)
     assert_equal(Float32(99) // Float32(-2), -50)
 
+    assert_equal(
+        Int32(2) // SIMD[DType.int32, 4](2, 4, -2, -4),
+        SIMD[DType.int32, 4](1, 0, -1, -1),
+    )
+    assert_equal(
+        2 // SIMD[DType.int32, 4](2, 4, -2, -4),
+        SIMD[DType.int32, 4](1, 0, -1, -1),
+    )
+
+    assert_equal(
+        Float32(3) // SIMD[DType.float32, 4](3, -4, 1, 5),
+        SIMD[DType.float32, 4](1, -1, 3, 0),
+    )
+    assert_equal(
+        3 // SIMD[DType.float32, 4](3, -4, 1, 5),
+        SIMD[DType.float32, 4](1, -1, 3, 0),
+    )
+
 
 def test_mod():
     assert_equal(Int32(99) % Int32(1), 0)