Stash radio settings per app (#1151)

* 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

firmware/application/apps/analog_audio_app.hpp

@@ -30,6 +30,7 @@
 #include "ui_record_view.hpp"
 #include "ui_styles.hpp"
 #include "app_settings.hpp"
+#include "radio_state.hpp"
 #include "tone_key.hpp"
 
 namespace ui {
@@ -155,6 +156,7 @@ class AnalogAudioView : public View {
    private:
     static constexpr ui::Dim header_height = 3 * 16;
 
+    RxRadioState radio_state_{};
     app_settings::SettingsManager settings_{
         "rx_audio", app_settings::Mode::RX,
         app_settings::Options::UseGlobalTargetFrequency};