msvc: set warning level to /W4 globally

And fix a bunch of warnings

src/yuzu_cmd/yuzu.cpp

@@ -265,7 +265,7 @@ int main(int argc, char** argv) {
                 password = match[2];
                 address = match[3];
                 if (!match[4].str().empty())
-                    port = std::stoi(match[4]);
+                    port = static_cast<u16>(std::stoi(match[4]));
                 std::regex nickname_re("^[a-zA-Z0-9._\\- ]+$");
                 if (!std::regex_match(nickname, nickname_re)) {
                     std::cout