CircularIndex: add static checks for index/size limits

The empty/full distinction fails to work if size matches the number of
representable positions for the index type.

Add a static check to ensure this invariant is met where possible.

src/hal/circular_buffer.h

@@ -2,6 +2,9 @@
 
 #include <stdint.h>
 #include <stddef.h>
+#ifndef __AVR__
+    #include <limits>
+#endif
 
 /// A generic circular index class which can be used to build circular buffers
 /// Can hold up to size elements
@@ -12,6 +15,11 @@
 template <typename index_t = uint_fast8_t, size_t size = 16>
 class CircularIndex {
 public:
+#ifndef __AVR__
+    static_assert(size <= std::numeric_limits<index_t>::max(),
+        "index_t is too small for the requested size");
+#endif
+
     constexpr inline CircularIndex()
         : tail(0)
         , head(0) {}