mem: rename Allocator primitives to alloc_bytes/dealloc_bytes (Phase 4 naming pulled forward, Agra-approved)

examples/0803-memory-push-context-with-arena.sx

@@ -10,7 +10,7 @@ main :: () -> void {
 
     new_ctx := Context.{ allocator = xx arena, data = context.data };
     push new_ctx {
-        ptr := context.allocator.alloc(128);
+        ptr := context.allocator.alloc_bytes(128);
         out("inside push\n");
     }
     out("after push\n");