Make allocate take a template type

So we use the right alignment

src/arena_allocator.cpp

@@ -67,7 +67,7 @@ void ArenaAllocator::reset() {
 void *ArenaAllocator::realloc(void *ptr, size_t old_size, size_t new_size,
                               size_t alignment) {
   if (ptr == nullptr) {
-    return allocate(new_size, alignment);
+    return allocate_raw(new_size, alignment);
   }
 
   if (new_size == old_size) {
@@ -119,7 +119,7 @@ void *ArenaAllocator::realloc(void *ptr, size_t old_size, size_t new_size,
   }
 
   // Growing but can't extend in place - need to allocate new space and copy
-  void *new_ptr = allocate(new_size, alignment);
+  void *new_ptr = allocate_raw(new_size, alignment);
   if (new_ptr && ptr) {
     // Copy all the old data since we're growing
     std::memcpy(new_ptr, ptr, old_size);