Improve error message for mandatory attributes after defaults

[Topgearfanboy]

Summary

When a mandatory attribute appears after an attribute with a default value or factory, the error message now includes which attribute has the default value. This makes it much easier to identify the problem and fix the attribute ordering.

Previously, the error message only mentioned the mandatory attribute that lacked a default:

No mandatory attributes allowed after an attribute with a default value or factory.  Attribute in question: Attribute(name='y', ...)

Now it also shows which attribute has the default:

No mandatory attributes allowed after an attribute with a default value or factory.  Attribute in question: Attribute(name='y', ...) appears after Attribute(name='x', default=None, ...)

This addresses the issue raised in #437 where users struggled to understand which attributes were out of order, especially in complex inheritance scenarios or when using field transformers.

Test plan

• Updated existing tests in tests/test_make.py and tests/test_hooks.py to match the new error message format
• All existing tests pass with the new message format
• The change is purely a message improvement with no behavior changes