making the switch from using async_std to tokio

**Is your feature request related to a problem? Please describe.**
Yes, it is related to a performance and ergonomics issue. Currently, RustScan uses async_std for asynchronous programming. While async_std is a great library, it has been observed that Tokio provides better performance and more ergonomic APIs in some cases.

**Describe the solution you'd like**
I would like RustScan to switch from async_std to Tokio for handling asynchronous tasks. This would involve refactoring the existing code that uses async_std to use Tokio instead. The goal is to improve the performance of RustScan and make the internal code more ergonomic (highly opinionated).

**Describe alternatives you've considered**
An alternative would be to continue using async_std and try to optimize the current implementation. However, given the reported performance and ergonomic advantages of Tokio, switching to Tokio seems pretty promising.

**Additional context**
For users who use this crate as a library, users of async std would not be able to use it, although tokio users would benefit greatly as there is no longer a need to startup an invisible background async_std runtime, and given that tokio is much more popular I belive this is worth it