Performance Improvements and Refactoring: Replace flume with crossbeam SegQueue

Hi, This PR improves performance in various parts of the code and includes some refactoring. Main changes are: 1. ~In the iouring driver, I removed two heap allocations, which simplifies the implementation and should slightly improve performance.~ (will send it in separate PR with correct Pin usage) 2. I removed flume. As the creator of the kanal, I respect the flume project as a safe channel implementation, but in this library, the channel structure is unnecessary and not required since it is effectively being used as a queue. Queues always outperform channels because they are simpler structures with fewer features. Using the lock-free crossbeam unbounded SegQueue should improve performance under high contention, as the use case does not require blocking recv, which is a channel feature. 3. Slight refactoring and improvements in other parts of project.