[PWGLF] Refactor and Optimize chk892flow.cxx for Improved Readability and Performance

[BongHwi]

• Code Cleanup:
  • Removed unnecessary includes (TMath.h, TDatabasePDG.h, TPDGCode.h).
  • Replaced TMath::Abs with standard std::abs for better portability.
  • Updated variable names to follow a consistent naming convention (e.g., DetId to lDetId).
• Performance Improvements:
  • Introduced the use of std::cos, std::atan2 instead of ROOT-specific functions for efficiency.
  • Optimized event selection by refactoring redundant configurations.
  • Replaced repeated calculations with pre-computed values where applicable.
• New Features:
  • Added configuration options for rotated background analysis, allowing flexibility in pion rotation settings.
  • Implemented histogram for tracking rotated background angles.
• Code Style and Readability:
  • Renamed and refactored several methods to improve clarity and consistency (GetCentrality → getCentrality, GetDetId → getlDetId).
  • Applied consistent formatting and spacing for better readability.
  • Improved logging messages for debugging purposes.