Apply clean code principles and fix all warnings
- Unified tracker and handler patterns with consistent interfaces
- Extracted methods following Single Responsibility Principle
- Added comprehensive JavaDoc documentation
- Fixed all IntelliJ warnings (null checks, always true conditions)
- Improved error handling and null safety
- Converted magic numbers/strings to constants
- Enhanced code readability and maintainability
For more information read project page https://github.com/sheduxdev/ExtraPlaceholders