Add explicit fmt:: and std:: to avoid ambiguous call

[LiAuTraver]

Use three major compilers (clang++ 19, msvc 2022, g++ 14) when std::format_to and fmt::format_to are both present, the call in

       return format_to(ctx.out(), "[my_type i={}]", my.i);

would be ambiguous. The reason is unknown(even if it's in fmt::formatter or std::formatter), but it's really easy to fix this. specify std:: or fmt:: before format_to will solve the problem.

[LiAuTraver]

Oops, it seems the f in fmt was eaten by commit message. never mind.😂

[gabime]

Thanks @LiAuTraver