* 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.
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Co-authored-by: kallanreed <kallanreed@outlook.com>
Add Gain control to the GPS Sim App .
(we are clonning the two previous PR's n #395 and #446 of the Replay App, correcting TX Gain control to this GPS Sim App )