Implement logging using built-in logging library

[ecarrenolozano]

This pull request refactors logging throughout the cache_manager package to use Python's standard logging module instead of the custom _log function. The changes improve consistency, flexibility, and integration with external logging systems. The main updates include replacing all _log calls with logger.debug, introducing module-level loggers, and removing _log imports.

Logging refactor in cache_manager/_cache.py:

• Replaced all occurrences of _log with logger.debug for logging messages throughout the Cache class and related functions. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31]
• Added a module-level logger to cache_manager/_cache.py and removed the _log import. [1] [2]

Logging refactor in cache_manager/_freshness.py:

• Replaced _log with logger.debug in the _check_etag function and removed the _log import. [1] [2]
• Added a module-level logger to cache_manager/_freshness.py.

API cleanup:

• Removed the log and _log exports from cache_manager/__init__.py to reflect the removal of the custom logging function.