feat(idempotency): add automatic priming for DynamoDB persistence store

[dcabib]

Description

Implements automatic class preloading via CRaC hooks for the powertools-idempotency-dynamodb module to improve SnapStart cold start performance.

This PR adds automatic priming support to complement the existing invoke priming that was implemented in #1861.

Changes

• ✅ Add ClassPreLoader.preloadClasses() call to DynamoDBPersistenceStore.beforeCheckpoint()
• ✅ Generate and include classesloaded.txt with 8,726 classes
• ✅ Add powertools-common dependency for ClassPreLoader
• ✅ Add Maven profile generate-classesloaded-file for regenerating the classes file
• ✅ Add unit tests for CRaC hooks (beforeCheckpoint() and afterRestore())
• ✅ Update Priming.md with idempotency-dynamodb example
• ✅ Add null check and logging for defensive error handling

Implementation Details

This implementation combines both priming strategies:

1. Invoke priming (already existed): Exercises DynamoDB SDK paths with PUT/GET/DELETE operations
2. Automatic priming (new): Preloads 8,726 classes from classesloaded.txt during SnapStart checkpoint

The combined approach ensures optimal cold start performance by:

• Warming up DynamoDB client connection pools
• Preloading all necessary classes into memory
• Exercising critical code paths before the snapshot is taken

Pattern Consistency

Follows the same pattern as implemented in:

• powertools-metrics (feat: Support CRaC and priming of powertools metrics and idempotency-dynamodb #1861)
• powertools-tracing (feat(crac): Support CRaC and priming of powertools tracing #2345)
• powertools-kafka (feat: add CRaC priming support to powertools-kafka module #2145)

Key differences justified for persistence layer:

• Exception handling: Wraps priming in try-catch to ensure checkpoint never fails (critical for persistence operations)
• Null check: Guards against disabled idempotency scenario
• Logging: Logs exceptions for debugging while maintaining fail-safe behavior

Testing

• ✅ Unit tests pass: testBeforeCheckpointDoesNotThrowException() and testAfterRestoreDoesNotThrowException()
• ✅ Example application builds successfully
• ✅ All existing tests continue to pass

Verification

To verify this works with SnapStart:

1. Deploy a Lambda function with SnapStart enabled using idempotency-dynamodb
2. Check CloudWatch Logs for priming execution during INIT phase
3. Observe reduced cold start times compared to non-primed deployments

Related Issues

Fixes #1997

Maintainer Confirmation

As confirmed by @phipag in #1997 (comment):

"Option 1 sounds good. Only add it in -dynamodb for now."

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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