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dereferencing an iterator from the right view of a bimap gives inconsisent results with using ->first and ->second #46

Description

@hoorayphyer

Boost version: 1.86
fmt version: 11.0
g++ version: Apple clang version 15.0.0 (clang-1500.3.9.4)
OS: macOS 14.1

Issue:
In the following code snippet

 boost::bimap<int, std::string> m;
 m.insert({1, "one"});

 for (auto iter = m.right.begin(); iter != m.right.end(); ++iter) {
    auto [k, v] = *iter;
    fmt::println("key = {}, val = {}", k, v);
    fmt::println("first = {}, second = {}", iter->first, iter->second);
  }

I'd expect the two ways to print the info regarding the order. Yet I observed

key = 1, val = one
first = one, second = 1

where apprently using structured binding gives the "wrong" result in the right view.

Expected behavior:
Dereferencing a right iterator should give consistent results with ->first and ->second. Otherwise, it leads to subtle errors to use bimap.right in any generic code where a map is being traversed using the structured binding, i.e. for (auto [k, v] : generic_map).

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