Rename ArenaAllocator -> Arena

src/metric.hpp

@@ -50,7 +50,7 @@
 #include <type_traits>
 #include <vector>
 
-#include "arena_allocator.hpp"
+#include "arena.hpp"
 
 namespace metric {
 
@@ -220,7 +220,7 @@ std::vector<double> exponential_buckets(double start, double factor, int count);
 // allocated in provided arena for zero-copy efficiency. The caller is
 // responsible for the arena's lifecycle. THREAD SAFETY: Serialized by global
 // mutex - callbacks need not be thread-safe
-std::span<std::string_view> render(ArenaAllocator &arena);
+std::span<std::string_view> render(Arena &arena);
 
 // Validation functions for Prometheus compatibility
 bool is_valid_metric_name(std::string_view name);