Fix: Add support for List<Integer> and other primitive wrapper lists

[wassertim]

Summary

Fixes #4 - Mapper generation now correctly handles List<Integer>, List<Double>, and other primitive wrapper lists.

Problem

The annotation processor was failing to generate valid mapper code when encountering List<Integer> fields, attempting to use a non-existent ListMapper class and causing compilation errors.

Root Cause

The TypeAnalyzer lacked a mapping strategy for lists of primitive wrapper types. It only handled:

• List<String> → STRING_LIST
• List<List<Number>> → NESTED_NUMBER_LIST
• List<@DynamoMappable> → COMPLEX_LIST

Lists of primitive wrappers fell through to COMPLEX_OBJECT, which incorrectly tried to generate mapper dependencies.

Solution

Core Changes

1. Added NUMBER_LIST mapping strategy (FieldInfo.java)

   • New enum value for handling lists of numeric types

2. Enhanced type detection (TypeAnalyzer.java)

   • Now detects numeric element types in lists and maps them to NUMBER_LIST strategy
   • Checks both wrapper types (Integer, Double, etc.) and primitives

3. Implemented code generation (FieldMappingCodeGenerator.java)

   • Serialization: Converts List<Integer> to DynamoDB list format (L) with number attributes (N)
   • Deserialization: Converts DynamoDB lists back to typed lists using appropriate numeric methods

Test Coverage

Added comprehensive integration tests (ListIntegerMappingTest.java):

• ✅ Basic List field mapping
• ✅ Round-trip conversion (serialize → deserialize)
• ✅ Null list handling
• ✅ Empty list handling

Generated Code Example

Before (compilation error):

private final ListMapper listMapper;  // ❌ ListMapper doesn't exist

After (working):

// Serialization
if (obj.getWaypointIndices() != null) {
    List<AttributeValue> list = obj.getWaypointIndices().stream()
        .map(val -> AttributeValue.builder().n(String.valueOf(val)).build())
        .collect(Collectors.toList());
    attributes.put("waypointIndices", AttributeValue.builder().l(list).build());
}

// Deserialization
List<AttributeValue> listValue = MappingUtils.getListSafely(attr);
if (listValue != null) {
    List<Integer> result = listValue.stream()
        .map(MappingUtils::getIntegerSafely)
        .filter(Objects::nonNull)
        .collect(Collectors.toList());
    builder.waypointIndices(result);
}

Test Results

All 27 integration tests pass, including 4 new tests for List mapping.