Add impl for TryFromSliceError

[newAM]

This implements defmt::Format for TryFromSliceError which enables code like this:

use core::convert::TryInto;

let foo: [u8; 5] = [0, 1, 2, 3, 4];
let bar: u32 = u32::from_be_bytes(defmt::unwrap!(foo[1..2].try_into()));

When it fails it looks like this:

ERROR panicked at 'unwrap failed: foo [1 .. 2].try_into()'
error: `TryFromSliceError(())`

Which is similar to what it looks like on std targets with .unwrap()

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: TryFromIntError(())', src/main.rs:5:35

[justahero]

Thanks!

bors r+

[bors]

Build succeeded:

• ci