[experimental] Experiment with these crates

- https://crates.io/crates/smol as a tokio replacement
- https://crates.io/crates/crossbeam for synchronization and concurrency primitives
- https://crates.io/crates/rayon it's best for parallel computing on iter. If we are to use a buffer instead of channels, we can use this to process parts of the buffer (packets) in parallel without the overhead of tokio

Review the three linked crates—smol, crossbeam, and rayon—and compare them with the project's current Tokio-based approach. The issue does not name files or tests; completion would require a decided experiment scope and evidence for whether these alternatives suit synchronization, concurrency, or parallel packet processing.

Written by the indexing model from the issue text.