refactor: use structured logging instead of print in letter_counting_environment.py

[alireza78a]

Summary

Replace all print() calls with proper logging in letter_counting_environment.py.

Problem

The file uses print() for config loading messages and import warnings, while already having logging imported and using self.logger elsewhere in the class.

Changes

• Added module-level logger = logging.getLogger(__name__)
• Replaced 5 print() calls with appropriate log levels:
  • logger.warning() for missing optional dependencies (NLTK, datasets)
  • logger.info() for successful config loading
  • logger.warning() for missing config file
  • logger.error() for config parsing errors
• No functional changes

Testing

• Change is logging-only with zero logic impact
• pre-commit checks passed