New 234-line test file for interpolate_fields functions:
- Tests single-field scalar interpolation (Temperature)
- Tests single-field vector interpolation (Displacement 2D/3D)
- Tests multi-field interpolation (Temperature + Displacement)
- Tests field value and gradient extraction
- Tests individual field extraction (interpolate_field)
- Tests value-only extraction (interpolate_field_value)
- Validates zero-allocation for all interpolation functions
- Tests NamedTuple return types with proper field structure
Comprehensive test ensuring field interpolation works correctly
for all field types and maintains zero-allocation performance.
Jukka Aho