Split the `frequenz.sdk.actor` package to its own repository

[llucax]

What's needed?

We need to allow cloud applications to be able to write actors without depending on the microgrid.

Proposed solution

Split the frequenz.sdk.actor package to its own repository:

• [x] ~See which namespace would be possible to use for the new python package: frequenz.actor would be the natural choice, but it is still a namespace for the many actor packages. frequenz.actor.core or frequenz.actor.base might be some options, although not that clear. Keeping frequenz.sdk.actor could be another option, but we need to see if it doesn't conflict with frequenz.sdk living in another package too. Another alternative could be frequenz.actors (in plural, as we already have with channels), but that might be a bit confusing that we have both frequenz.actor and frequenz.actors packages.~ We can use the frequenz.actor package.
• [x] Create the new repository ~frequenz-actor-python~ frequenz-core-python
• [ ] Move the code there
• [ ] Release a v1.0.0 version (we want to ensure stability from day one, as we are stabilizing all the base repos).
• [ ] Remove the code from the SDK and depend on the new repo

Use cases

All the cloud apps.

Alternatives and workarounds

For now we've been copying protobuf files from the common API repo to the API repos that should depend on common to break the dependency, but this is clearly not sustainable.

Additional context

This is a very complicated, multi-dimensional, problem, involving many parts. Is part (and one way) to solve the dependency conflict of the SDK depending on the microgrid API v0.15 (and common v0.4) and the new API clients depending on common v0.5.

[shsms]

I like frequenz.actor.base, because it is the base class for all actors. but works badly for namespaced imports from frequenz.actor import base.

Maybe frequenz.actor.actor_base?

[llucax]

Maybe, what about frequenz.actor.actor? It is a bit redundant but it should work more naturally with the imports.

I will try if there is any way to still use the frequenz.actor module, that is definitely the ideal, but I don´t have very high expectations to succeed.

[shsms]

it would be actor inception 3 levels deep:

from frequenz.actor import actor

class A(actor.Actor):

[llucax]

[llucax]

I just did a test and we can use frequenz.actor :tada:

As long as only one wheel is defining frequenz/actor/__init__.py it seems to be fine.

[llucax]

This will actually be moved to the new core repository, as having a repo just for one class doesn't seem to have a lot of sense... Updating the issue title and description.