Python: fix: Preserve class type in experimental_class decorator to avoid type inference issues (microsoft#6709)

### Motivation and Context

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Closes microsoft#6707 

### Description

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- Introduce `TypeVar` `T` bounded to `type` to ensure the decorator
maintains the class type.
- Modify the `experimental_class` decorator to use the bounded `TypeVar`
for accurate type hinting.


### Contribution Checklist

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- [ ] The code builds clean without any errors or warnings
- [ ] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [ ] All unit tests pass, and I have added new tests where possible
- [ ] I didn't break anyone 😄

Author: miladh

python/semantic_kernel/utils/experimental_decorator.py

@@ -1,6 +1,9 @@
 # Copyright (c) Microsoft. All rights reserved.
 
 from collections.abc import Callable
+from typing import TypeVar
+
+T = TypeVar("T", bound=type)
 
 
 def experimental_function(func: Callable) -> Callable:
@@ -16,7 +19,7 @@ def experimental_function(func: Callable) -> Callable:
     return func
 
 
-def experimental_class(cls: type) -> type:
+def experimental_class(cls: T) -> T:
     """Decorator to mark a class as experimental."""
     if isinstance(cls, type):
         if cls.__doc__: