Fix Python 3.14 compatibility for modelclass decorator (KeyError: 'annotations')

[justinpolygon]

This PR addresses the breakage reported in #902, where Python 3.14's deferred annotation evaluation change (PEP 649) causes a KeyError when importing modules like RESTClient due to direct access to cls.__dict__["__annotations__"].

Background:

In Python 3.14, PEP 649 changes how type annotations are handled: they are now evaluated lazily (deferred) rather than eagerly at definition time. Annotations are stored internally via a new __annotate__ function (not for direct use), and the __annotations__ attribute is a descriptor that computes the annotation dictionary on access. This improves performance but alters runtime behavior. So, we currently directly check cls.__dict__["__annotations__"] and it fails in 3.14 with KeyError because __annotations__ is no longer a key in the class's __dict__ since it's a computed property.

Changes:

• Updated modelclass to use typing.get_type_hints(cls) for version-agnostic annotation retrieval. This evaluates annotations on-demand in 3.14 while working identically in older versions (3.8+).
• Corrected the attribute filtering logic: The original inspect.isroutine(a) (with a as str) always passed; now checks the actual class attribute to exclude methods properly.
• No impact on existing functionality.

Testing:

• Tested via Docker across Python 3.8, 3.9, 3.10, 3.11, 3.12, 3.13, and 3.14 with aggs endpoint samples.
• Verified no regressions in positional/keyword init for models like Agg.
• Confirmed fix resolves import errors in 3.14.
• Backwards Compatibility is fully preserved.