Refactor: decouple COS and auth from FleetHandler

[ElePT]

Summary

FleetHandler was doing too much: auth setup, COS credential resolution, and CE API calls. This PR splits those responsibilities apart. build_ce_auth is a new shared factory in clients.py that returns a ready (ApiClient, IBMCloudClientProvider). On the COS side, build_cos_client(project) is a standalone factory that fetches HMAC credentials from the CE secret and returns a ready JobCOS. FleetsRunner initializes the two independently via _get_handler() and _get_cos().

As part of this PR work I found that the swagger Configuration class used a shallow-copy singleton, so multiple FleetHandler instances were mutating each other's IAM token dict. This is now fixed by assigning fresh dicts instead of mutating. FleetHandler now just takes the pre-built ApiClient and stays a pure CE API wrapper

Details and comments

I am leaving the PR as a draft because I am having issues testing it on the demo branch, I will make it ready for review once I have verified that it works.

The goal of this and the follow-up PR is to enable the following flow at job creation time (rough implementation) without unnecessarily calling the FleetsRunner or the FleetHandler:

code_engine_project = select_ce_project(compute_profile)
cos = build_cos_client(code_engine_project)
cos.upload_fileobj(fileobj=..., bucket_name=code_engine_project.cos_bucket_user_data_name, key=f"jobs/{job.id}/arguments.json")

[Tansito]

Thanks for the PR @ElePT in essence I think it's the correct path to follow! A couple of minor comments that doesn't change the implementation but I think they are worth it:

• We are building factories in the __init__ files to avoid local imports like the one we have in build_ce_auth. You can use get_runner or get_arguments_storage as an example.
• I would like to propose change build_ce_auth and build_cos_client names by get_* to maintain consistency along all our factories.
• Maybe not for this PR, totally up to you here, I saw that in build_ce_auth we are returning a Tuple. Maybe it's better to return an object in this case as it can be confusing that a Factory returns a tuple here (it's also something we can do later if we want to move forward with this, no problem, it almost a refactor).

[ElePT]

Suggestions applied @Tansito, including the refactoring you suggested (returning a CEAuth object instead of a tuple). Let me know what you think!

[Tansito]

Pretty cool thank you much @ElePT 🎉