fix: handle DynamoDB creation timestamp precision

[kiwigitops]

Summary

• add ApproximateCreationDateTimePrecision to DynamoDB stream records
• parse and round-trip millisecond and microsecond creation timestamps when precision is present
• add a regression test for a microsecond timestamp payload

Testing

• go test ./events -run 'TestDynamoDB'\n\nFixes [BUG] ApproximateCreationDateTime from DynamoDBStreamRecord in milliseconds when originating from Kinesis, not seconds. #478

[codecov-commenter]

Codecov Report

❌ Patch coverage is 64.28571% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.81%. Comparing base (87e344b) to head (3c1aeaf).

Files with missing lines	Patch %	Lines
events/dynamodb.go	64.28%	11 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #633      +/-   ##
==========================================
- Coverage   75.12%   74.81%   -0.32%     
==========================================
  Files          36       37       +1     
  Lines        1419     1461      +42     
==========================================
+ Hits         1066     1093      +27     
- Misses        274      285      +11     
- Partials       79       83       +4     

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