feat: add PollFd, PrioQNode and PrioQueue

include/ring.h

@@ -0,0 +1,39 @@
+#ifndef FROSTBYTE_RING_H
+#define FROSTBYTE_RING_H
+
+#include "types.h"
+
+/*
+ * RingBuffer: a fixed-capacity byte circular buffer over a caller-supplied
+ * backing array. No heap dependency, so it is safe to use for early
+ * interrupt-driven queues (keyboard scancodes, serial RX) that need to
+ * exist before the kernel heap is initialised.
+ */
+
+typedef struct RingBuffer {
+    uint8* data;
+    usize capacity;
+    usize head;   /* next byte to read */
+    usize count;  /* bytes currently queued */
+} RingBuffer;
+
+void ringInit(RingBuffer* r, uint8* backingBuffer, usize capacity);
+void ringClear(RingBuffer* r);
+
+bool ringIsEmpty(const RingBuffer* r);
+bool ringIsFull(const RingBuffer* r);
+usize ringCount(const RingBuffer* r);
+usize ringCapacity(const RingBuffer* r);
+usize ringFreeSpace(const RingBuffer* r);
+
+/* Single-byte push/pop. Push returns false (buffer unchanged) when full;
+   pop returns false (out untouched) when empty. */
+bool ringPush(RingBuffer* r, uint8 byte);
+bool ringPop(RingBuffer* r, uint8* out);
+
+/* Bulk transfer. Writes/reads as many bytes as fit/are available (may be
+   fewer than requested) and returns the count actually transferred. */
+usize ringWrite(RingBuffer* r, const uint8* data, usize len);
+usize ringRead(RingBuffer* r, uint8* data, usize len);
+
+#endif