Senders like `std``::``execution``::``just`, `std``::``execution``::``then`, and `std``::``execution``::``let_value` take some arguments which can be chosen fairly freely. Some of these arguments may be allocator-aware to offer control over their respective allocation needs. Carefully using allocators can allow, e.g., using standard container types without using global `operator` `new``()`/`operator` `delete``()`.