The goal of this PR is to handle the case where scheduler send 404 when trying to get allocations of unallocated / wrong instance

Related ClickUp, GitHub or Jira tickets : ALEPH-597

Self proofreading checklist

• The new code clear, easy to read and well commented.
• New code does not duplicate the functions of builtin or popular libraries.
• An LLM was used to review the new code and look for simplifications.
• New classes and functions contain docstrings explaining what they provide.
• All new code is covered by relevant tests.

Changes

This pull request introduces changes to improve error handling and data type flexibility in the scheduler service and related models. The key updates include handling 404 errors gracefully when fetching allocation information and updating type annotations to allow None values for allocation-related fields.

Error handling improvements:

• src/aleph/sdk/client/services/scheduler.py: Updated the get_allocation method to handle 404 errors by returning None when allocation information cannot be found on the scheduler. Introduced ClientResponseError for error handling.

Data type flexibility:

• src/aleph/sdk/types.py: Modified the allocations field in the InstanceWithScheduler model to be Optional[AllocationItem], allowing it to represent cases where allocation information is unavailable.

Typing updates:

• src/aleph/sdk/client/services/scheduler.py: Added Optional to type imports to support the updated type annotations.