toolkit-helpers: formatSecurityDiff ignores nested templates

[kaizencc]

Describe the bug

In the DiffFormatter, we have options to formatSecurityDiff and formatStackDiff. For the stack diff, nestedStackTemplates can be provided via property and this becomes part of the stack diff:

const nextDiff = this.formatStackDiffHelper(
        nestedStack.deployedTemplate,
        nestedStack.physicalName ?? nestedStackLogicalId,
        nestedStack.nestedStackTemplates,
        options,
      );

For the security diff, this isn't considered at all, so it will always ignore nested stacks and only diff on the root stack.

We need to consider nested stacks for the security diff as well.

Regression Issue

• Select this option if this issue appears to be a regression.

Last Known Working CDK Version

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Expected Behavior

n/a

Current Behavior

n/a

Reproduction Steps

n/a

Possible Solution

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Additional Information/Context

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CDK CLI Version

2.1006.0

Framework Version

No response

Node.js Version

Node 20

OS

MacOS

Language

TypeScript

Language Version

No response

Other information

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