Explain Mutex vs RWMutex in the `sync` package.

Mutex enforces exclusive access, while RWMutex allows multiple simultaneous readers or one exclusive writer.

sync.Mutex locks critical sections so only one goroutine can execute them at a time. sync.RWMutex has RLock() and Lock(). If your workload is read-heavy, RWMutex drastically reduces lock contention because concurrent readers don't block each other. However, if writes are frequent, the overhead of managing read states in RWMutex can make it slower than a standard Mutex.