feat(custom-resource): upgrade to python runtime 3.13 for custom resources (#35342)

### Reason for this change
- Current custom resource handlers are using Python 3.9 and 3.11 runtimes
- Python 3.9 reaches EOL in October 2025
- Need to upgrade to Python 3.13 for better stability and continued support
- Affects multiple custom resource handlers including aws-ecs/drain-hook-provider, aws-eks/kubectl-provider, and others



### Description of changes
- Updated Python runtime from 3.9/3.11 to 3.13 in config.ts for generated bundle functions
- Modified runtime settings in:
  - notifications-resource-handler.ts
  - instance-drain-hook.ts
- Updated aws-eks-v2-alpha custom resource handler runtime
- Updated integration tests and snapshots



### Validation
- Deployed integration tests across multiple regions to verify functionality
- Verified Lambda Python 3.13 availability across required regions




### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: abidhasan-aws

packages/@aws-cdk-testing/framework-integ/test/aws-appconfig/test/integ.configuration.js.snapshot/aws-appconfig-configuration.assets.json

@@ -936,7 +936,7 @@
       "Arn"
      ]
     },
-    "Runtime": "python3.11",
+    "Runtime": "python3.13",
     "Timeout": 900
    },
    "DependsOn": [

packages/@aws-cdk-testing/framework-integ/test/aws-appconfig/test/integ.configuration.js.snapshot/aws-appconfig-configuration.template.json

@@ -529,7 +529,7 @@
       "Arn"
      ]
     },
-    "Runtime": "python3.11",
+    "Runtime": "python3.13",
     "Timeout": 900
    },
    "DependsOn": [