transparent operator like `less<void>` is not functionally usable with bimap

The current implementation is not allow to use transparent comparator/hash operator functionality.

```
boost::bimap>> test;

std::string stg;
test.right.find(stg); // error
```

The compile error message is [the following](https://godbolt.org/z/1sKaWEM3x):
```
/opt/compiler-explorer/libs/boost_1_80_0/boost/bimap/container_adaptor/associative_container_adaptor.hpp:194:17: error: no matching function for call to object of type 'boost::bimaps::container_adaptor::detail::key_to_base_identity'
this->template functor()(k)
```

Reproduce the failure from the provided Godbolt example, then inspect boost/bimap/container_adaptor/associative_container_adaptor.hpp at line 194 and the key_to_base_identity call mentioned in the diagnostic. Trace how test.right.find(stg) handles the transparent comparator and verify that this expression compiles successfully with the reported bimap declaration.

Written by the indexing model from the issue text.