Feature/conversion entrypoints spike

[YunaBraska]

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Motivation

Expanded streaming coverage to ensure the new stream-based JSON/XML paths behave correctly with deeply nested data, unicode, nulls, and XML-derived structures. This guards against regressions after the streaming refactors.

Changes

• Added complex object/array streaming cases to JsonDecoderTest (nested objects/arrays, unicode, nulls, mixed primitives).
• Added nested XML streaming scenario in TypeMapTest to validate streamPairs traversal of attributes, nested lists/maps, and role extraction without full materialization.
• Adjusted assertions to align with current XML decoding shape (attributes and text nodes wrapped in TypeList).

Success Check

• ./mvnw -q test passes.