[alloy] Certain specializations of `alloy::adaptor` incorrectly fetches "pointer to reference"

[saki7]

C++ standard forbids taking pointer to a reference.

• std_pair.hpp: When the element of the pair is a reference type, the current implementation tries to fetch "pointer to the member of reference"
  • The specialization for std::pair should be aligned with std_tuple.hpp, where the tuple version correctly delegates to std::get.
• adapt.hpp: ditto, but this version can't simply use std::get for user-defined types; additional metafunction needed.
• std_tuple.hpp: The implementation is correct, but the noexcept specifier is missing.

@yaito3014 Could you take a look into this?