Add IDCClient() singleton feature

[LennyN95]

No need for a global client = IDCClient() call, instead IDCClient.client() can be used directly. Upon first call a new IDCClient instance will be initialized and reused for all following calls.

[vkt1414]

@LennyN95 do you recommend any tutorials or books to learn more about singletons?

[fedorov]

@LennyN95 I don't object in principle, but can you give the rationale for adding this feature?

I don't think I ever had a need to create more than one client. Or maybe that's exactly the point - to prevent user from creating multiple clients, since this should not ever be needed, but indeed can easily be done before this change?

I assume you will resolve the conflicts.

[LennyN95]

This here gives an excellent overview!

Note, I didn't implement an actual singleton but rather a singleton factory method, which I believe is the most suited for our use case. It simplifies access while not impacting flexibility and testability.

[LennyN95]

Sure @fedorov, I've multiple reasons in mind:

1. As you said, prevention from user's unnecessarily instantiating multiple instances.
2. No need for a global client variable if we can hold it internally.
3. Direct access via IDCClient.client().<any_api_method> saves one extra line.

[fedorov]

@LennyN95 I resolved the conflicts.

[fedorov]

@LennyN95 I hope you can look into CI errors!

[LennyN95]

@fedorov I added this import such that we can import IDCClient directly, instead of importing index and then accessing it via index.IDCClient. I see this got removed, is this because we have any rule that prevents adding such imports on the package level or did it just got lost in the process? I prefer this way as it simplifies importing a lot and enhances ux in my opinion but I'm open for counter-arguments ;)

Some of the errors are related to the now missing import, so I wait for your reply before fixing them.

Thx for looking into this!!

[LennyN95]

The linter doesn't like the unused import... I push a workaround, let me know what you think ;)

[fedorov]

Indeed, I just accepted the corrections that we proposed by the linter/ruff. Looks good to me!