fix: resolve cppcheck warnings for const pointer and static functions

Co-authored-by: aider (deepseek/deepseek-reasoner) <aider@aider.chat>

src/looper.c

@@ -135,7 +135,7 @@ int process_callback(jack_nframes_t nframes, void *arg) {
                                                  memory_order_acquire);
     if (r != NULL) {
       if (state == STATE_LOOPING && atomic_load(&channels[c].loop_count) > 0) {
-        float *outf = (float *)out;
+        const float *outf = (const float *)out;
         ring_write(r, outf, nframes);
       }
     }

src/ringbuffer.c

@@ -30,7 +30,7 @@ void ring_destroy(RingBuf *r) {
   r->capacity = 0;
 }
 
-size_t ring_readable(const RingBuf *r) {
+static size_t ring_readable(const RingBuf *r) {
   size_t h = load_head(r);
   size_t t = load_tail(r);
   if (h >= t)
@@ -39,7 +39,7 @@ size_t ring_readable(const RingBuf *r) {
     return r->capacity - (t - h);
 }
 
-size_t ring_writeable(const RingBuf *r) {
+static size_t ring_writeable(const RingBuf *r) {
   return r->capacity - 1 - ring_readable(r);
 }
 

src/ringbuffer.h

@@ -13,8 +13,6 @@ typedef struct {
 
 int  ring_init(RingBuf *r, size_t capacity);
 void ring_destroy(RingBuf *r);
-size_t ring_readable(const RingBuf *r);
-size_t ring_writeable(const RingBuf *r);
 size_t ring_write(RingBuf *r, const float *data, size_t count);
 size_t ring_read(RingBuf *r, float *data, size_t count);