* add a little Stash utility.
* add radio state RAII helper.
* first part of radio_state changes
* add radio_state_ to rest of apps
* fix freq_step and format
* fix unused ui_sigfrx: corrected sample rate, added back freq setting
* Use receiver/transmitter models everywhere
* Run formatter
* Fix a copy-paste bug, make transmitter_model actually set tx_gain.
---------
Co-authored-by: kallanreed <kallanreed@outlook.com>