perf(rpc server): Improve crossplatform basic workpool performance

[InKryption]

Currently the .basic WorkPool is effectively just a naive but cross-platform blocking loop; it used a threadpool before it was simplified in #477 for the purposes of facilitating the architecture re-design. It should still remain simple, and not be required to rely too heavily on platform-specific optimizations.
Other strategies that rely more on platform-specific optimizations similar to io_uring on linux should be implemented as separate WorkPool backends.

This issue can be closed with a PR that succeeds in enhancing the performance .basic backend.