refactor: move fas_queue extern to fas_queue/queue.h

Create internal header with forward declaration and include of This
reduces visible definitions in public API.

Author: gin66

src/StepperISR.h

@@ -2,7 +2,7 @@
 
 #include "FastAccelStepper.h"
 #include "fas_arch/common.h"
-#include "fas_queue/base.h"
+#include "fas_queue/queue.h"
 
 #if defined(SUPPORT_AVR)
 #include "pd_avr/avr_queue.h"
@@ -18,8 +18,6 @@
 #error "Unsupported architecture"
 #endif
 
-extern StepperQueue fas_queue[NUM_QUEUES];
-
 #if defined(SUPPORT_CPU_AFFINITY)
 void fas_init_engine(FastAccelStepperEngine* engine, uint8_t cpu_core);
 #else

src/fas_queue/queue.h

@@ -0,0 +1,11 @@
+#ifndef FAS_QUEUE_QUEUE_H
+#define FAS_QUEUE_QUEUE_H
+
+#include "fas_arch/common.h"
+#include "fas_queue/base.h"
+
+class StepperQueue;
+
+extern StepperQueue fas_queue[NUM_QUEUES];
+
+#endif