This commit adds logging to embassy-dfu-usb which helps with debugging issues such as https://github.com/embassy-rs/embassy/issues/3536. It also cleans up a few repeated code blocks and avoid re-initialising the local buffer for every iteration.
This makes location info in defmt logs point to the code calling the macro,
instead of always to fmt.rs as before. Fix works with nightlies
starting with today's, and stable 1.81+.
