Feat/pause tracking

[Jozys]

This pull request introduces several changes to enhance the activity tracking functionality, including the addition of pause/resume capabilities, updates to the tracking state, and improvements to the user interface.

Enhancements to Activity Tracking Functionality:

• Added a new ActivityBroadcastReceiver in AndroidManifest.xml to handle pause and stop actions for activity tracking.
• Updated the tracking state to include isPaused and durationMillis fields in TrackingState and modified the copyWith method accordingly. [1] [2]
• Introduced a togglePauseTracking method in TrackingViewModel to handle pausing and resuming of activities, replacing the previous pauseTracking method.
• Modified the startTimer and updateDuration methods in TrackingViewModel to work with durationMillis instead of a string duration.

User Interface Improvements:

• Updated ActiveTracking widget to display durationMillis and handle paused state, including changes to the pause button icon. [1] [2]
• Enhanced TrackingRecording widget to show the elapsed time and current speed, considering the paused state. [1] [2] [3] [4]
• Adjusted TrackingFinished widget to display the total duration in milliseconds. [1] [2] [3]

Code Refactoring:

• Updated various files to replace string duration with durationMillis and to include isPaused state where necessary. [1] [2] [3] [4]
• Simplified event handling in TrackingViewModel by using constants from the Event class.