feat: replace go-logging with logrus and expose native logger

[ArditZubaku]

• Replace github.com/op/go-logging with github.com/sirupsen/logrus
• Expose goesl.Logger directly for full logrus functionality access
• Maintain backward compatibility with existing logging functions
• Add support for structured logging with fields and context
• Preserve environment variable configuration (GOESL_LOG_LEVEL, GOESL_LOG_FORMAT)
• Use logrus native ParseLevel() for better error handling
• Enable thread-safe logging operations with built-in atomics
• Update documentation with advanced usage examples
• Add Go module support (go.mod/go.sum)

Breaking changes: None - all existing logging function calls remain compatible
New features: Direct access to logrus logger for advanced logging capabilities