Compare large arrays in memory-bounded chunks

[Silvren]

Summary

• lazily open NetCDF job result datasets instead of eagerly loading them
• compare compatible numerical arrays above a 64 MiB threshold in bounded rectangular chunks
• stream mismatch counts and absolute-difference statistics without full-size intermediate arrays
• preserve rtol, atol, NaN, complex-number, and pixel_tolerance behavior
• keep the existing detailed comparison path for smaller arrays

Testing

• python -m pytest tests/testing -q (86 passed)
• pre-commit run --files CHANGELOG.md openeo/testing/results.py tests/testing/test_results.py

Fixes #871