Extract browser detection functions to separate file

[bhouston]

Description

This PR is a follow-up to PR #373, extracting the browser detection functions from the SessionTracker class into a separate module.

Changes

1. Created a new browserDetectors.ts file in the lib directory

   • Moved all browser detection functions to this file
   • Exported the BrowserInfo interface and detection functions

2. Updated SessionTracker and sessionStart to import from the new file

   • Simplified the SessionTracker class by removing the inlined functions
   • Maintained the same functionality and API

Benefits

• Improved code organization and separation of concerns
• Made the SessionTracker class more focused on its primary responsibility
• Made browser detection functions more reusable

Testing

• All tests pass
• Browser functionality works as expected