feat!: migrate from akka to pekko

[limansky]

This closes #358

I've found that examples/src-jvm2 folder is not used in compilation, so I didn't changed examples there.

[ex0ns]

Thanks a lot, very good catch !
I'm going to push a fix on main to solve the issue with src-jvm2 but we should definitely update it as well (I'm almost done with the mill changes)

[ex0ns]

@limansky I believe we made a typo when upgrading to Scala 3, by naming the folder src-jvm2 instead of src-jvm-2 those files were indeed not used anymore.
This is now fixed, but it means that we will have to migrate them to Pekko as well.

The easiest way I found to run a bunch of example is to run them directly in mill:

./mill -i 'examples.jvm[].console' # scala 2
./mill -i 'examples.jvm[3.3.7].console' # scala 3

Then you can run any bot from here:

new LmgtfyBot(<BOT TOKEN>).run()
new EchoBot(<BOT TOKEN>).run()

You can run the token from the env to avoid it being in the REPL's history

[ex0ns]

I tested this on a few webhook example as well as more classic example (lmgtfy, echo, commands) and this is working well.

Thank you very much for your work, I will now merge and release 7.0.0