Fix ResourceType.architecture()

[hartikainen]

JobRequirements calls ResourceType.architecture(), but the public ResourceType enum does not currently implement it, causing accelerator requirements to fail with an AttributeError.

This PR:

• Adds default host architecture handling for accelerators.
• Maps GB{200,300} to Architecture.ARM and fixed-host. accelerators to Architecture.HASWELL
• Leaves LOCAL_GPU architecture unspecified unless provided explicitly.
• Adds regression coverage for inference and validation.