Camera stream optimizations (#156)

Simplified the logic for the mjpeg stream decoding and display, along
with adding text for bandwidth and FPS
* Use stream builder instead of flutter hooks
* Remove StreamManager, instead have one change notifier to hold the
state and decoding streams
* Only start a camera stream when the widget becomes focused
* Rebuild the widget when focus changes, automatically restarting
streams properly

lib/services/log.dart

@@ -62,6 +62,10 @@ class Log {
   void debug(dynamic message, [dynamic error, StackTrace? stackTrace]) {
     log(Level.debug, message, error, stackTrace);
   }
+
+  void trace(dynamic message, [dynamic error, StackTrace? stackTrace]) {
+    log(Level.trace, message, error, stackTrace);
+  }
 }
 
 Log get logger => Log.instance;