ref_ptr: nullptr_t support, return ref shared_ptr

static_vector, small_vector: drop usage of std::aligned_storage

- new library: ref_ptr

- ufunction: improve empty {} init
- utility: add transfer_view_as

- [type_traits]: add add copy_cv, add concepts

- [utility]: add transfer_view
- [rand_dist]: drop precision in favor of perf in fast_real
- add benchmarks

new lib: rand_dist

new lib: opt_ref_buffer

flat_map/set: fix const_pointer typedef
generator: more robust noexcept guarantees
any: fix scope of nullptr_t (fixes newer gcc and clang builds)
mem_streambuf::get_conatiner: first resize then swap

expected: fix <void, E>, add emplace to all

- generator: return type

- flat_map/set: hint-based insert, ready_tag for sorted init
- cmake: fix deprecation warning

expected: add "getters" for void value and error

- ufunction: allow binding to copies of source functions

- generator: improve iterator interface when yielding non-copyable items

generator: fix clang crash on exception