Regression in boost::hash with version 1.81.0

We are noticing regression with `boost::hash` when used with `std::u16string` in boost 1.81.0 version and compared to 1.78.0. As per the 1.81.0 documentation, it seems there are major changes in `boost::hash` and the performance with string should be improved. Any thoughts on this regression?

Sample program -
```
#include
#include
#include

int main()
{
// Start the timer
auto start = std::chrono::high_resolution_clock::now();

for(int i = 0; i < 10; i++)
{
boost::hash()(u"hello");
}

// End the timer
auto end = std::chrono::high_resolution_clock::now();

// Calculate the duration
std::chrono::duration duration = end - start;

// Print the duration in seconds
std::cout << "Execution time: " << (duration.count())/10 << " seconds." << std::endl;

return 0;
}
```

Link 1.78.0 - https://godbolt.org/z/ManWPoK8j
Link 1.81.0 - https://godbolt.org/z/hejbsfhc6