test: validate bounded DynamoDB ingestion

[j6k4m8]

Summary

• replace permissive DynamoDB writer mocks with strict recording fakes
• verify ingestion uses one writer per table and writes every edge and node request
• cover bounded behavior across a larger dataframe without cloud resources

[codspeed-hq]

Merging this PR will not alter performance

✅ 17 untouched benchmarks

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_{Comparing fix/dynamodb-bulk-ingestion-74 (af5e5f7) with master (fe117e0)}