fix(custom-resource-handlers): better fallback for require failures (#31571)

### Issue # (if applicable)

Closes #30067.

### Reason for this change

Fallback to existing AWS SDK import misses a rare/flaky edge case where the npm install passes, but the subsequent `require` fails

### Description of changes

Fall back to the pre-existing AWS SDK if requiring the latest version fails

### Description of how you validated changes

- Fixed no-op test "installs the latest SDK"
- Added test "falls back to installed sdk if require fails"

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

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

Author: glitchassassin

packages/@aws-cdk-testing/framework-integ/test/aws-events-targets/test/logs/integ.log-group.js.snapshot/asset.eafc02f6925151c95ac6a6ae81a3e36d4cf4e77db52eec8e467ce2a69454a41a.bundle/index.js renamed to packages/@aws-cdk-testing/framework-integ/test/aws-elasticloadbalancingv2-actions/test/integ.cognito.js.snapshot/asset.358df072f638d226bc60515a98fa15305e91193108367a0fa01dc626fb9b07d6.bundle/index.js

@@ -827,7 +827,7 @@
      "S3Bucket": {
       "Fn::Sub": "cdk-hnb659fds-assets-${AWS::AccountId}-${AWS::Region}"
      },
-     "S3Key": "9e8936ba1db43e0919ba2fc8265d50686eeaca82830c471ff8b7b0672c5970ec.zip"
+     "S3Key": "aa903f33cd9fe411974d9bc150e046dc03dd0d7ee4d5934f7e2c172b2f61650e.zip"
     },
     "Handler": "index.handler",
     "Role": {

packages/@aws-cdk-testing/framework-integ/test/aws-elasticloadbalancingv2-actions/test/integ.cognito.js.snapshot/asset.9e8936ba1db43e0919ba2fc8265d50686eeaca82830c471ff8b7b0672c5970ec/index.js renamed to packages/@aws-cdk-testing/framework-integ/test/aws-elasticloadbalancingv2-actions/test/integ.cognito.js.snapshot/asset.aa903f33cd9fe411974d9bc150e046dc03dd0d7ee4d5934f7e2c172b2f61650e/index.js

@@ -903,7 +903,7 @@
      "S3Bucket": {
       "Fn::Sub": "cdk-hnb659fds-assets-${AWS::AccountId}-${AWS::Region}"
      },
-     "S3Key": "9e8936ba1db43e0919ba2fc8265d50686eeaca82830c471ff8b7b0672c5970ec.zip"
+     "S3Key": "aa903f33cd9fe411974d9bc150e046dc03dd0d7ee4d5934f7e2c172b2f61650e.zip"
     },
     "Handler": "index.handler",
     "Role": {