fix(data-classes): keep the value of large DynamoDB numbers

[chiruu12]

Issue number: closes #8512

Summary

Changes

_deserialize_n used to count characters and slice the string when a number was longer than 38. The minus sign and the decimal point were counted as digits, and removing trailing zeros by slicing changed the magnitude.

It now parses with Decimal(value). When the coefficient has more than 38 digits, it is normalized with a 38-digit context, which moves trailing zeros into the exponent. DYNAMODB_CONTEXT.create_decimal then accepts it without raising Rounded (#4845) and the value is unchanged. Numbers with 38 digits or fewer go through as before.

Tests:

• New parametrized test in tests/unit/shared/test_dynamodb_deserializer.py covering a negative 38-digit number, a 38-digit decimal, the value from DynamoDBRecord throws decimal.Rounded for large numbers (over 38 digits) #4845 and a 38-digit number times 1000. All four fail on develop.
• test_dynamodb_stream_record_deserialization_large_int asserted that a 47-digit number came back as a 38-digit one. Its expected value is now the original number.
• test_dynamodb_stream_record_deserialization_large_int_without_trailing_zeros uses a value with more than 38 significant digits, which DynamoDB can't store. It now expects the number rounded to 38 digits at the same magnitude, instead of the first 38 characters.

User experience

Before:

>>> TypeDeserializer().deserialize({"N": "-12345678901234567890123456789012345678"})
Decimal('-1234567890123456789012345678901234567')

After:

>>> TypeDeserializer().deserialize({"N": "-12345678901234567890123456789012345678"})
Decimal('-12345678901234567890123456789012345678')

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.92%. Comparing base (3311cc1) to head (130217c).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8513   +/-   ##
========================================
  Coverage    96.92%   96.92%           
========================================
  Files          317      317           
  Lines        15910    15911    +1     
  Branches      1398     1398           
========================================
+ Hits         15421    15422    +1     
  Misses         353      353           
  Partials       136      136           

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[sonarqubecloud]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

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

See analysis details on SonarQube Cloud

[leandrodamascena]

Thanks for the fix, @chiruu12! I pushed a small follow-up after testing some edge cases. Normalization now raises Inexact if it would change the value, and scientific zero values like 0E+0 are preserved. I also added regression tests for these cases, including numbers inside collections and stream images.

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[boring-cyborg]

Awesome work, congrats on your first merged pull request and thank you for helping improve everyone's experience!

[powertools-for-aws-oss-automation]

Awesome work, congrats on your first merged pull request and thank you for helping improve everyone's experience!