fix(dynamodb-enhanced): Fix NPE in ConverterUtils and EnhancedType for null and wildcard types

[abhu85]

Summary

This PR fixes two NullPointerException bugs in the DynamoDB Enhanced Client:

1. Issue NullPointerException in DefaultAttributeConverterProvider when validating null Double values #6639: ConverterUtils.validateDouble() and validateFloat() throw NPE when the input is null due to auto-unboxing before the null check.

2. Issue NPE when calling hashCode() on wildcard DynamoDB EnhancedType #5890: EnhancedType.hashCode() and equals() throw NPE when dealing with wildcard types like List<?>, where rawClass is null.

Root Cause

Issue #6639

The validateDouble and validateFloat methods used Double.isNaN(input) and Double.isFinite(input) which auto-unbox the Double/Float wrapper to a primitive, causing NPE when input is null.

Issue #5890

For wildcard types (e.g., List<?>), EnhancedType stores rawClass = null. The hashCode() method called rawClass.hashCode() and equals() called rawClass.equals() without null checks.

Changes

• ConverterUtils.java: Add early return for null input in validateDouble() and validateFloat()
• EnhancedType.java: Add null checks for rawClass in both hashCode() and equals() methods
• ConverterUtilsTest.java: New test class with 10 tests covering null, valid, NaN, and infinite values
• EnhancedTypeTest.java: Add 2 tests for wildcard type handling in hashCode() and equals()

Test Plan

• All 10 new ConverterUtilsTest tests pass
• All 25 EnhancedTypeTest tests pass (including 2 new tests)
• Tests verify: null input handling, valid values, NaN rejection, infinity rejection, wildcard equality

Test Commands

./mvnw test -pl services-custom/dynamodb-enhanced -Dtest=ConverterUtilsTest,EnhancedTypeTest
# Tests run: 35, Failures: 0, Errors: 0, Skipped: 0

Fixes #6639
Fixes #5890