Remove app::utils helpers with zero fleet call sites after the app_common
merge (as_u8s, hexdump, add_overflow/overflow_error, try_get/try_get_ref,
constrain_value_in_range_static — a template-bounds reimplementation of
std::clamp) and the unused app_clock milliseconds alias. This drops several
heavy includes from a header every consumer compiles.
Rewrite deferrer as a stdlib scope guard that owns the callable directly
(template<F>, non-copyable/non-movable) instead of type-erasing through
std::move_only_function/std::function, so it never heap-allocates. The 3
call sites (band max32664d) are unchanged via CTAD.
crosstyan
