Windows Support for Custom Networking (Secondary CIDR for Pod IPs)

**Description:**
Currently, the Custom Networking feature in the AWS VPC CNI plugin is only supported for Linux nodes. This feature allows pods to be assigned IP addresses from secondary CIDR ranges using ENIConfig, instead of consuming IPs from the primary node subnet.

However, Windows nodes in EKS do not support Custom Networking, and Windows pods always receive IP addresses from the node subnet.

**Problem Statment:**

In environments running Windows workloads on EKS, this limitation can lead to rapid IP exhaustion in the worker node subnet, especially in clusters with high pod density or limited subnet CIDR ranges.

Since Windows pods must consume IPs from the same subnet as the node, it becomes difficult to scale Windows workloads without expanding the node subnet.

This creates operational challenges such as:
Frequent subnet IP exhaustion
Need for larger node subnets, which may not always be feasible in existing VPC designs
Reduced flexibility in network segmentation and IP management

**Expected Behavior / Feature Request:-**
It would be very helpful if Custom Networking support could be extended to Windows nodes, similar to how it works for Linux nodes.

The issue does not name repository files, tests, or implementation entry points. Start by locating the existing Linux Custom Networking and ENIConfig implementation, then investigate the AWS EKS Windows networking constraints; done means defining and implementing equivalent secondary-CIDR pod IP support for Windows nodes.

Written by the indexing model from the issue text.