[C++]: Identity cast for `Time64Scalar` and `Time32Scalar` fails

[sgilmore10]

Describe the bug, including details regarding any error messages, version, and platform.

The identity cast for Time64Scalar and Time32Scalar no longer works as of arrow version 16.1.0.

If this executable:

#include "arrow/scalar.h"
#include "arrow/result.h"
#include "arrow/status.h"
#include <iostream>

arrow::Status test_scalar_cast() {
    auto type =  arrow::time64(arrow::TimeUnit::type::MICRO);//arrow::time64(arrow::TimeUnit::type::MICRO);
    ARROW_ASSIGN_OR_RAISE(auto scalar, arrow::MakeScalar<int64_t>(type, int64_t(1e6)));   
    std::cout << "Casting from time64[us] scalar to time64[us] scalar..." << std::endl;
    ARROW_ASSIGN_OR_RAISE(auto cast_result, scalar->CastTo(type));
    return arrow::Status::OK();
}

int main(int argc, char *argv[]) { 
    auto status = test_scalar_cast();
    if (!status.ok()) {
        std::cout << "Cast failed with message: " << status.message() << std::endl;
    } else {
        std::cout << "Success!" << std::endl;
    }
    return 0;
}

is linked against arrow version 16.1.0, the identity cast fails:

$ ./main
Casting from time64[us] scalar to time64[us] scalar...
Cast failed with message: casting scalars of type time64[us] to type time64[us]

However, if the executable is linked against arrow version 16.0.0, the identity cast works as expected:

$ ./main
Casting from time64[us] scalar to time64[us] scalar...
Success!

I did some code archeology, and I believe this bug was introduced in #40237.

Component(s)

C++

[mapleFU]

I'd like to take a fix here

[pitrou]

Issue resolved by pull request 45370
#45370