feat: Logging Hook

[NeaguGeorgiana23]

This PR

• Logging Hook Support:
  • Implements LoggingHook as mentioned in the OpenFeature specification.
  • Introduces LogLevel and LogCallback for pluggable loggers with standard stream defaults.
  • Supports all 4 hook stages (Before, After, Error, Finally) with optional evaluation context logging.
• Exception Hierarchy:
  • Adds structured OpenFeatureException hierarchy with associated ErrorCode values.
• Serialization:
  • Adds string conversions (ToString()) and streaming operators for EvaluationContext, Reason, ErrorCode, and Value.

Related Issues

Fixes #138

[coderabbitai]

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