optree: Hierarchical Runtime Configuration Management

Provides tools for managing nested, multi-level configuration systems with runtime mutability, type validation, and default value management. Supports creating hierarchical options managers with customizable validators for scalar and vector types (numeric, character, logical), enumerated values, bounded ranges, and complex structures like XY pairs. Options can be dynamically modified at runtime while maintaining type safety through validator functions, and easily reset to their default values when needed.