[Radio] Adjust value limits for mix sources and update UI for LSs, CFs & telem. (#5445)

* [firmware][ARM] Adjust some value limits for mix sources and update editing UI for LSs, CFs, & telem. bars:
    * Increase timer limits to +/-8:59:59 when used with LSs, CFs, & bars;
    * Increase Lua script output limits to +/-30K;
    * Trim limits based on extended limit model setting;
    * Limit TX voltage to 25.5;
    * Limit TX time comparison value to 29:59m;
    * Use proper GVar limits (user-configured), display precision, & unit in LSs & telem. bars;
    * Display timer values properly with hours (instead of mmm:ss).

* [firmware] getTimerString() would fail with times >= 100min if hours weren't shown.

* Fix builds w/out GVars.

radio/src/gui/common/arm/widgets.cpp

@@ -142,6 +142,11 @@ void drawSourceCustomValue(coord_t x, coord_t y, source_t source, int32_t value,
       lcdDrawNumber(lcdNextPos, y, gpsData.numSat, flags);
     }
   }
+#endif
+#if defined(GVARS)
+  else if (source >= MIXSRC_FIRST_GVAR && source <= MIXSRC_LAST_GVAR) {
+    drawGVarValue(x, y, source - MIXSRC_FIRST_GVAR, value, flags);
+  }
 #endif
   else if (source < MIXSRC_FIRST_CH) {
     lcdDrawNumber(x, y, calcRESXto100(value), flags);