*: specialize fmt::formatter<> for formatting using {fmt}

*: specialize fmt::formatter<> for formatting using {fmt}

in {fmt} v9, fmt::formatter<> is not defined automatically for
the types with operator<<, we need to define them explictly. so in this
change, the types printed using `fmt::print()` or `fmt::format()` are
equiped with fmt::formatter<> to appease {fmt} v9.

Signed-off-by: Kefu Chai <tchaikov@gmail.com>