Incorrect Documentation for `LRUKReplacer::Evict()` Return Type

[MikhailWahib]

The documentation for LRUKReplacer::Evict() (/src/buffer/lru_k_replacer.cpp) incorrectly describes its return type. The function signature returns std::optional<frame_id_t>, but the docstring states:

@return true if a frame is evicted successfully, false if no frames can be evicted.

Suggested Fix

Update the @return description in the docstring to:

/**
 * @return The evicted frame ID if successful, std::nullopt if no frames can be evicted.
 */