Drift detection for IPv6CidrBlock doesn't process correctly for AWS::EC2::Subnet

### Name of the resource

AWS::EC2::Subnet

### Resource Name

AWS::EC2::Subnet

### Issue Description

When processing drift detection for the IPv6CidrBlock attribute on a `AWS::EC2::Subnet` resource, IPv6 shorthand addressing used in the cloudformation templates (say through the use of a string or the `Fn::Cidr` intrinsic) is not properly compared to the full IPv6 notation on the resource.

For example, the following are not treated as equal.

### Expected Behavior

IPv6 addresses that mean the same thing (i.e. equivalent) to be treated as equal

### Observed Behavior

Expected
```json
{
"AssignIpv6AddressOnCreation": true,
"AvailabilityZone": "ap-southeast-2a",
"CidrBlock": "10.0.0.0/24",
"Ipv6CidrBlock": "2406:da1c:a1e:1234:0:0:0:0/64",
"Tags": [
{
"Key": "Name",
"Value": "MySubnet-A"
}
],
"VpcId": "vpc-aaaaaaaa"
}
```

Actual
```json
{
"AssignIpv6AddressOnCreation": true,
"AvailabilityZone": "ap-southeast-2a",
"CidrBlock": "10.0.0.0/24",
"Ipv6CidrBlock": "2406:da1c:a1e:1234::/64",
"Tags": [
{
"Key": "Name",
"Value": "MySubnet-A"
}
],
"VpcId": "vpc-aaaaaaaa"
}
```

### Test Cases

Specify IPv6 shorthand addresses in a cloudformation template, deploy the subnet and run drift detection. All subnets should drift.

### Other Details

_No response_

No repository files, tests, or code entry points are named. Reproduce drift detection for AWS::EC2::Subnet with the shorthand and expanded IPv6CidrBlock values shown, then trace how those values are compared; done means equivalent IPv6 addresses are treated as equal and no longer report drift.

Written by the indexing model from the issue text.