Concurrent Graph Operations

Explain race conditions and the need for synchronization in a multi-threaded context.

Implement a thread pool to parallelize graph construction by processing multiple vector insertions concurrently.

Use a `pthread_rwlock_t` (Read-Write Lock) to allow multiple concurrent searches while ensuring exclusive access for graph modifications.

Refactor graph data structures to use C11 atomic types (`<stdatomic.h>`) for lock-free counters and flags where appropriate.

Analyze and prevent potential deadlocks in concurrent search and insertion scenarios.