Add --version CLI flag

[jiribenes]

In tooling (especially in effekt-lang/effekt-vscode#20), it would be nice to know the version of the current Effekt executable so that we can offer a newer version.

We already surface the version number via the REPL, but it would be much easier if tooling could rely on an easily parseable format.

Specification

When the user specifies the --version flag, the program prints the effekt.util.Version.effektVersion and exits successfully. Note that the successful exit is very important, this allows us to automate a bunch of things.

I'm not really sure if it's better to implement this in Kiama for REPLConfig directly or here for EffektConfig.

Alternatives

We could also just assume every user installed Effekt via npm and check the version there, but that feels extremely finicky to me -- it would also break my own workflow, as my Effekt is never installed via npm :)

Related work

For example in npm and node:

$ npm --version
10.5.0

$ node --version
v20.12.2