fix(event-handler): replace Optional[list] with list | None in graphql_appsync/base.py docstrings

Update docstring code examples to use modern Python 3.10+ syntax:
- Optional[list] -> list | None
- Remove unused `from typing import Optional` from examples

Part of #8088

Signed-off-by: hirenkumar-n-dholariya <hirenkumarnd@gmail.com>

Author: hirenkumar-n-dholariya

aws_lambda_powertools/event_handler/graphql_appsync/base.py

@@ -25,16 +25,14 @@ def resolver(self, type_name: str = "*", field_name: str | None = None) -> Calla
         Examples
         --------
         ```python
-        from typing import Optional
-
         from aws_lambda_powertools.event_handler import AppSyncResolver
         from aws_lambda_powertools.utilities.data_classes import AppSyncResolverEvent
         from aws_lambda_powertools.utilities.typing import LambdaContext
 
         app = AppSyncResolver()
 
         @app.resolver(type_name="Query", field_name="getPost")
-        def related_posts(event: AppSyncResolverEvent) -> Optional[list]:
+        def related_posts(event: AppSyncResolverEvent) -> list | None:
             return {"success": "ok"}
 
         def lambda_handler(event, context: LambdaContext) -> dict:
@@ -76,16 +74,14 @@ def batch_resolver(
         Examples
         --------
         ```python
-        from typing import Optional
-
         from aws_lambda_powertools.event_handler import AppSyncResolver
         from aws_lambda_powertools.utilities.data_classes import AppSyncResolverEvent
         from aws_lambda_powertools.utilities.typing import LambdaContext
 
         app = AppSyncResolver()
 
         @app.batch_resolver(type_name="Query", field_name="getPost")
-        def related_posts(event: AppSyncResolverEvent, id) -> Optional[list]:
+        def related_posts(event: AppSyncResolverEvent, id) -> list | None:
             return {"post_id": id}
 
         def lambda_handler(event, context: LambdaContext) -> dict:
@@ -127,16 +123,14 @@ def async_batch_resolver(
         Examples
         --------
         ```python
-        from typing import Optional
-
         from aws_lambda_powertools.event_handler import AppSyncResolver
         from aws_lambda_powertools.utilities.data_classes import AppSyncResolverEvent
         from aws_lambda_powertools.utilities.typing import LambdaContext
 
         app = AppSyncResolver()
 
         @app.async_batch_resolver(type_name="Query", field_name="getPost")
-        async def related_posts(event: AppSyncResolverEvent, id) -> Optional[list]:
+        async def related_posts(event: AppSyncResolverEvent, id) -> list | None:
             return {"post_id": id}
 
         def lambda_handler(event, context: LambdaContext) -> dict: