sqlpp::optional is an alias for std::optional for C++17 and beyond.
Otherwise, it is a simple and incomplete backport.
For older versions of C++, the library offers simple back
Similar for string_view and span.
Leak: The sqlite3 connection handle destructor was
accidentally turned into a default constructor during the
migration of repositories.
Replaced the sqlite3 raw pointer with a unique_ptr to prevent
this kind of accident.
Changed sqlite3 usage tests to be linked into one executable.
This provokes multiple definition errors for non-inlined free
functions.
Also ran clang-format on the changed headers.
