Refactor examples to build a single binary

[cBournhonesque]

We previously did a refactor where the example mode was entirely defined by features. (i.e. start as client if only the client feature is enabled, etc.).
This caused some issues:

• if you want to run as server and then as client, it causes a recompile because the set of features is different, which is annoying
• on Windows, this would cause 2 binaries to be created with the same path, which causes an error.
• Rust Analyzer uses the default features, so if you compile the binaries with the 'client' or 'server' feature it would cause RustAnalyzer to rebuild afterwards

To avoid this, I am changing all examples to run with all features enabled, and the user can choose the 'mode' of operation via a CLI argument.