feat(mixins-preview): generate metrics facades

[leonmk-aws]

Description of changes

Automatically generate metrics facades.
Usage:

// L1 / L2 Lambda
const fn: lambda.Function

// Scoped metrics from L2
const fnMetrics = LambdaMetrics.fromFunction(fn);

// Create metric
const metric = fnMetrics.metricErrors();

// Use metric as usual
new cloudwatch.Alarm(this, 'L2ErrorAlarm', {
  metric: metric
  alarmName: 'MixinsPreview-L2-Errors',
  threshold: 5,
  evaluationPeriods: 1,
  comparisonOperator: cloudwatch.ComparisonOperator.GREATER_THAN_THRESHOLD,
});

Generated code structure:

// Generated structure (abbreviated)
export class LambdaMetrics {
  // Factory: create metrics from a Function reference (auto-fills dimensions)
  static fromFunction(ref: IFunctionRef): LambdaMetrics.FunctionNameMetrics;
}

export namespace LambdaMetrics {
  // Per-function metrics (dimension: FunctionName)
  class FunctionNameMetrics {
    constructor(props: { functionName: string });
    metricInvocations(options?: MetricOptions): IMetric;
    metricErrors(options?: MetricOptions): IMetric;
    metricDuration(options?: MetricOptions): IMetric;
    metricThrottles(options?: MetricOptions): IMetric;
    // ... 8 more metric methods
  }

  // Per-function + resource metrics (dimensions: FunctionName, Resource)
  class FunctionNamePerResourceMetrics {
    constructor(props: { functionName: string; resource: string });
    metricInvocations(options?: MetricOptions): IMetric;
    // ... + metricProvisionedConcurrencyUtilization
  }

  // Per-version metrics (dimensions: ExecutedVersion, FunctionName, Resource)
  class ExecutedVersionPerFunctionNamePerResourceMetrics { /* ... */ }

  // Account-level metrics (no dimensions)
  class AccountMetrics {
    constructor();
    metricInvocations(options?: MetricOptions): IMetric;
    metricUnreservedConcurrentExecutions(options?: MetricOptions): IMetric;
    // ...
  }
}

Description of how you validated changes

Added unit and integration test

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

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

[aws-cdk-automation]

(This review is outdated)

[github-actions]

⚠️ Experimental Feature: This security report is currently in experimental phase. Results may include false positives and the rules are being actively refined.
This security report is NOT a review blocker. Please try merge from main to avoid findings unrelated to the PR.

---

	Tests	Passed ✅	Skipped	Failed
Security Guardian Results	48 ran	48 passed

Test	Result
No test annotations available

• View Security Guardian Results

[github-actions]

⚠️ Experimental Feature: This security report is currently in experimental phase. Results may include false positives and the rules are being actively refined.
This security report is NOT a review blocker. Please try merge from main to avoid findings unrelated to the PR.

---

	Tests	Passed ✅	Skipped	Failed
Security Guardian Results with resolved templates	48 ran	48 passed

Test	Result
No test annotations available

• View Security Guardian Results with resolved templates

✅ Updated pull request passes all PRLinter validations. Dismissing previous PRLinter review.

[mrgrain]

Can you move the codegen directly into spec2cdk and just have the most minimal wrapper code in mixins-preview. I think it was a mistake to have it not in the shared package. See the cfn prop mixins on how this can be done generating into any destination.

Also, should we have a separate preview/alpha package? Feels like we have now decided that mixins-preview should be removed soon.