Integrate micronucleus into the cargo buildsystem.

# ./.cargo/config.toml
[target.'cfg(target_arch = "avr")']
# Choose a default "cargo run" tool
runner = "elf2uf2-rs -d"

At the time of writing, it's not possible to configure micronucleus as "cargo run" tool, because micronucleus can't read from elf files.

You can use avr-objcopy to prepare the firmware file yourself though:

avr-objcopy --output-target=ihex target/avr-attiny85/release/attiny85-hello-world.elf target/avr-attiny85/release/attiny85-hello-world.hex
micronucleus --timeout 60 --run --no-ansi target/avr-attiny85/release/attiny85-hello-world.hex