esp-println: Add auto-detect feature

[MabezDev]

In the flasher stub we have some code to detect (from ROM code) which transport method is connected: https://github.com/esp-rs/esp-flasher-stub/blob/e9b61293aa181a6ef8ffb326ce4360cf2f1162c3/src/lib.rs#L43-L77.

Maybe we can adapt this to use in esp-println, so that no output method feature is required. It might help in cases such as esp-rs/esp-wifi-sys#452.

One thing I'm not so sure about is when this detection should occur, I think my initial instinct would be to make it lazy and check on first access and then keep using that method until reset.

[bjoernQ]

Good idea. Should probably be a new default feature since detecting it at runtime would require to have code for both in the resulting binary - not a lot of code however