Macros are not self-contained

Exported Rust macros (per best "hygiene" practices) should not require any external paths to be brought into local scope. So, if a crate exports a macro, that macro should only use fully-qualified items from the same crate, or more specifically - use the `$crate` metavariable per [docs](https://veykril.github.io/tlborm/decl-macros/minutiae/hygiene.html#crate).

At least `declare_stack_allocator_struct!` macro uses non-fully-qualified identifiers like `declare_stack_allocator_struct!` inside, requiring crate users to `use` it, making the code unclean and possibly error prone.