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/pocsag_app.hpp

@@ -29,6 +29,7 @@
 
 #include "log_file.hpp"
 #include "app_settings.hpp"
+#include "radio_state.hpp"
 #include "pocsag.hpp"
 #include "pocsag_packet.hpp"
 
@@ -59,6 +60,7 @@ class POCSAGAppView : public View {
     bool logging() const { return check_log.value(); };
     bool ignore() const { return check_ignore.value(); };
 
+    RxRadioState radio_state_{};
     app_settings::SettingsManager settings_{
         "rx_pocsag", app_settings::Mode::RX};