Documentation: Add Comprehensive Docstrings

[lv416e]

Problem

CodeRabbit's automated review detected that docstring coverage is currently 0.00%, which is below the required threshold of 80.00%. This affects code maintainability and developer experience.

Current State

• Most classes, methods, and functions lack documentation comments
• No standardized docstring format is in place
• Difficult for new contributors to understand API contracts and usage

Proposed Solution

Add comprehensive docstrings to the codebase following a consistent format (e.g., Doxygen-style for C++):

Priority Areas

1. High Priority - Public APIs

   • include/evolab/schedulers/mab.hpp - MAB scheduler classes
   • include/evolab/core/concepts.hpp - Core concepts
   • include/evolab/local_search/ - Local search operators
   • include/evolab/operators/ - Genetic operators

2. Medium Priority - Implementation Classes

   • Scheduler implementations
   • Problem-specific implementations
   • Helper classes

3. Lower Priority

   • Internal utility functions
   • Test helpers

Documentation Standards

Each public class/function should include:

• Brief description
• Template parameter documentation
• Parameter descriptions
• Return value documentation
• Usage examples (where helpful)
• Exception specifications

Example Format

```cpp
/// @brief Adaptive operator selector using Multi-Armed Bandit algorithms
///
/// Automatically selects the best-performing crossover operator based on
/// historical performance data using UCB or Thompson Sampling.
///
/// @tparam SchedulerType The MAB scheduler type (UCBScheduler or ThompsonSamplingScheduler)
/// @tparam Problem The optimization problem type
///
/// @example
/// ```cpp
/// UCBOperatorSelector selector(2, 2.0, rng);
/// selector.add_operator(OrderCrossover(), "OX");
/// selector.add_operator(PMXCrossover(), "PMX");
/// ```
template <typename SchedulerType, typename Problem>
class AdaptiveOperatorSelector {
// ...
};
```

Related

• Detected in PR feat(mab): integrate Lin-Kernighan with Multi-Armed Bandit scheduler #28 (feat/lk-mab-integration)
• Part of improving overall code quality and maintainability

Acceptance Criteria

• Docstring coverage reaches at least 80%
• All public APIs have comprehensive documentation
• Consistent documentation format across codebase
• CodeRabbit checks pass without docstring warnings

Notes

This is a large task that should be broken down into smaller PRs, potentially one per module or directory.