feat(core): make Buffer.IsFreed nil-safe

Co-Authored-By: Virgil <virgil@lethean.io>

buffer.go

@@ -123,6 +123,9 @@ func (b *Buffer) Len() int {
 //	buffer := NewBuffer(4)
 //	if buffer.IsFreed() { ... }
 func (b *Buffer) IsFreed() bool {
+	if b == nil {
+		return true
+	}
 	return b.freed.Load()
 }
 

buffer_test.go

@@ -71,6 +71,15 @@ func TestBufferUseAfterFreePanics(t *testing.T) {
 	})
 }
 
+func TestBufferIsFreedIsNilSafe(t *testing.T) {
+	t.Parallel()
+
+	var nilBuffer *Buffer
+	if !nilBuffer.IsFreed() {
+		t.Fatal("expected nil buffer to report freed")
+	}
+}
+
 func TestCStringRoundTrip(t *testing.T) {
 	t.Parallel()