replace Printf with std::format where possible

[rmpowell77]

Noticed that we have this in SetupMarchers.cpp:186

            for (int i = 0; i < n; ++i) {
                wxString buffer;
                if (letr >= 26) {
                    buffer.Printf(wxT("%c%c%u"), 'A' + letr - 26, 'A' + letr - 26, i);
                } else {
                    buffer.Printf(wxT("%c%u"), 'A' + letr, i);

We should try to replace Printf with std::format where we can.