addition: allocator generator and functions

include/lae_arena.h

@@ -30,6 +30,15 @@ typedef struct {
     };
 } ArenaPointer;
 
+typedef struct {
+    bool is_valid;
+
+    union {
+        ArenaErr err;
+        Allocator allocator;
+    };
+} ArenaAllocResult;
+
 typedef struct {
     bool is_valid;
     union {
@@ -54,4 +63,6 @@ ArenaSizeResult arena_get_align_padding(Arena *arena, size_t alignment);
 // I shouldn't cover.
 ArenaErr arena_ensure_capacity(Arena *arena, size_t size, size_t alignment);
 
+ArenaAllocResult arena_get_allocator(Arena *arena);
+
 #endif // !RENA_H