[core] add is_sdk_model check and tests

[iscai-msft]

fixes #41438

[Copilot]

Pull Request Overview

This PR adds a new function, is_sdk_model, to help determine if an object qualifies as an SDK model.

• Introduces the is_sdk_model function with a clear docstring outlining its purpose
• Implements a check for either a "_is_model" attribute or "_attribute_map" presence to signal an SDK model

Comments suppressed due to low confidence (1)

sdk/core/azure-core/azure/core/serialization.py:133

• [nitpick] The docstring for 'is_sdk_model' uses ':type obj: any' which might be clearer if it matches the function's type annotation (i.e., using 'Any' with proper casing) for consistency.

def is_sdk_model(obj: Any) -> bool:

[iscai-msft]

/check-enforcer override