mlxrunner: Refcount pinned tensors

Otherwise, it is error prone to manage multiple components working
with the same tensor.

x/mlxrunner/mlx/array.go

@@ -20,7 +20,7 @@ import (
 type Array struct {
 	ctx    C.mlx_array
 	name   string
-	pinned bool
+	pinned int
 }
 
 var arrays []*Array
@@ -129,7 +129,7 @@ func (t *Array) Clone() *Array {
 func Pin(s ...*Array) {
 	for _, t := range s {
 		if t != nil {
-			t.pinned = true
+			t.pinned++
 		}
 	}
 }
@@ -138,7 +138,7 @@ func Pin(s ...*Array) {
 func Unpin(s ...*Array) {
 	for _, t := range s {
 		if t != nil {
-			t.pinned = false
+			t.pinned--
 		}
 	}
 }
@@ -148,7 +148,7 @@ func Unpin(s ...*Array) {
 func Sweep() {
 	n := 0
 	for _, t := range arrays {
-		if t.pinned && t.Valid() {
+		if t.pinned > 0 && t.Valid() {
 			arrays[n] = t
 			n++
 		} else if t.Valid() {
@@ -175,7 +175,7 @@ func (t *Array) String() string {
 func (t *Array) LogValue() slog.Value {
 	attrs := []slog.Attr{
 		slog.String("name", t.name),
-		slog.Bool("pinned", t.pinned),
+		slog.Int("pinned", t.pinned),
 	}
 	if t.Valid() {
 		attrs = append(attrs,