Prevent status bar animations on timer updates

[rajbos]

This pull request introduces a caching mechanism for detailed token statistics in the CopilotTokenTracker class to improve performance and reduce unnecessary recalculations. The main change is the introduction of a lastDetailedStats property, which stores the most recently calculated stats and reuses them when available. Additionally, the updateTokenStats method now supports a silent mode to suppress progress updates during background refreshes.

Caching and performance improvements:

• Added a lastDetailedStats property to cache the most recently calculated DetailedStats and avoid redundant recalculations in the CopilotTokenTracker class. [1] [2] [3]
• Modified the updateTokenStats method to accept a silent parameter, allowing background updates without showing progress in the status bar. [1] [2]