aws-ecs: missing `scaleInAfter` property in `ManagedInstancesCapacityProvider`

### Describe the feature

AWS recenty introduced the [`scaleInAfter`](https://docs.aws.amazon.com/AWSCloudFormation/latest/TemplateReference/aws-properties-ecs-capacityprovider-infrastructureoptimization.html#aws-properties-ecs-capacityprovider-infrastructureoptimization-properties) property for ECS Managed Instances, but that's not currently supported in the [`ManagedInstancesCapacityProvider`](https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_ecs.ManagedInstancesCapacityProvider.html) L2 construct.

AWS News: [Amazon ECS Managed Instances adds configurable scale-in delay](https://aws.amazon.com/about-aws/whats-new/2025/11/amazon-ecs-managed-instances-configurable-scale-in-delay/)

### Use Case

Support latest ECS features.

### Proposed Solution

_No response_

### Other Information

_No response_

### Acknowledgements

- [ ] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### AWS CDK Library version (aws-cdk-lib)

2.223.0

### AWS CDK CLI version

2.1031.2

### Environment details (OS name and version, etc.)

Ubuntu 24.04

Start at the TypeScript implementation and tests for the ManagedInstancesCapacityProvider L2 construct, then compare its supported properties with the AWS CloudFormation ECS infrastructure optimization reference. Trace how construct properties map to the synthesized ECS capacity provider and verify that scaleInAfter is accepted and emitted with the expected value.

Written by the indexing model from the issue text.