feat(ptr): not_null_ptr, fix not_null hash, make_not_null, release and swap

[codethinki]

Summary

• not_null_ptr<T> = not_null<T*>. The argument names the pointee like move_ptr<T> and unique_not_null<T>, const goes in the argument: not_null_ptr<T const>. The converting constructor gives not_null_ptr<T> -> not_null_ptr<T const>.
• fix: std::hash<not_null> used not_null::pointer, which does not exist, so no not_null was hashable. It hashes the value of get() now (the raw pointer for unique_not_null).
• fix: make_not_null had Adapt without a default and not deducible, so no call compiled. The order is <Null = nullptr, Adapt = false, T> now: make_not_null(&x), make_not_null<VK_NULL_HANDLE>(handle). It is constexpr, and noexcept only when the constructor is (debug builds check the value).
• fix: release() on a raw pointer did not compile: the noexcept spec called T::release() and the if constexpr had no else.
• fix: swap() only took the default Null and Adapt.

For cth_engine, which replaces its not_null<X const*> with not_null_ptr<X const>.

Test plan

• gcc and clang, debug and release: 271/271, 7 new tests (hash, release, make_not_null, custom Null swap, const conversion)
• CI: Linux gcc/clang, Windows msvc/clang