Support float decimal formatting

[David-OConnor]

Desired effect. Code:

println!("\nDoor open. Conf: {:.2}", confidence as f32 / 255.);

Expected: Confidence is printed as 2 decimal places like in Rust std println. Actual:

error: unknown display hint: ".2"

         = help: `defmt` uses a slightly different syntax than regular formatting in Rust. See https://defmt.ferrous-systems.com/macros.html for more details.

I think this (And apeing std::println more broadly) would make this lib easier to use etc. Or at least in the error, show the correct way to do it. Ty!

Love this lib btw; it's a core part of my embedded experience, and I love how defmt::println etc are very similar to the std equivalents.

[jonathanpallant]

Agreed. I often find myself wanting this.