core: Put Python version as a project requirement so it is considered by ruff (#26608)

Ruff doesn't know about the python version in
`[tool.poetry.dependencies]`. It can get it from
`project.requires-python`.

Notes:
* poetry seems to have issues getting the python constraints from
`requires-python` and using `python` in per dependency constraints. So I
had to duplicate the info. I will open an issue on poetry.
* `inspect.isclass()` doesn't work correctly with `GenericAlias`
(`list[...]`, `dict[..., ...]`) on Python <3.11 so I added some `not
isinstance(type, GenericAlias)` checks:

Python 3.11
```pycon
>>> import inspect
>>> inspect.isclass(list)
True
>>> inspect.isclass(list[str])
False
```

Python 3.9
```pycon
>>> import inspect
>>> inspect.isclass(list)
True
>>> inspect.isclass(list[str])
True
```

Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com>

libs/core/langchain_core/outputs/chat_result.py

@@ -1,4 +1,4 @@
-from typing import List, Optional
+from typing import Optional
 
 from pydantic import BaseModel
 
@@ -18,7 +18,7 @@ class ChatResult(BaseModel):
     for more information.
     """
 
-    generations: List[ChatGeneration]
+    generations: list[ChatGeneration]
     """List of the chat generations.
     
     Generations is a list to allow for multiple candidate generations for a single