test: enhance ManifestListReaderV2Test and unified test architecture (#168)

### V2 Manifest Format Support
  - **Add V2 Non-Partitioned Tests for ManifestListReader**.

  ### Unified Test Architecture
- **ManifestListReaderTestBase**: New base class providing shared
functionality for all manifest reader tests
- **Consistent Inheritance**: Both V1 and V2 test classes inherit from
`TempFileTestBase` for uniformity
- **Unified Helper Methods**: Common `TestManifestListReading()` and
`TestNonPartitionedManifests()` utilities

Author: HeartLinked