In order to https://github.com/microsoft/vcpkg/pull/28988 vcpkg's sqlite-orm port, a few things needed to be addressed:

• pinned appveyor test environment to vcpkg 2023.01.09
• made type_is_nullable<> a specializable struct again
• examples are now fully linkable again: chrono_binding.cpp, nullable_enum_binding.cpp, pointer_passing_interface.cpp (those examples - wrongly commented out the main() function)
• updated unit test framework to Catch2 v3 (https://github.com/fnc12/sqlite_orm/issues/1114)
• updated clang-format lint action on github
• removed dangling submodule reference (https://github.com/fnc12/sqlite_orm/issues/1107)
• made all examples compilable with Visual C++ 2015 Update 3

Update (2023-01-15): Currently unit tests fail with Visual C++ 2015 Update 3 as the minimal C++14 base compiler, as Catch2 v3 now requires a fully compliant C++14 compiler. Let's see what the decision is on the [feature request] (https://github.com/catchorg/Catch2/issues/2624) I made.

Update (2023-01-24): Now that Catch2 v3 requires a conforming C++14 compiler, legacy compilers like Visual C++ 2015 Update 3 can't be used anymore for compiling the unit tests. The library itself and its examples are still usable with legacy compilers.