Core: Respect partition evolution in inspect.partitions

[010Soham]

What does this change do?

• Build the inspect.partitions schema using only the partition specs present in the selected snapshot’s manifests, so newer partition fields don’t appear as None for older snapshots.
• Normalize partition comparisons in integration tests to ignore trailing None fields from dropped partition columns.

Why is this needed?

• Partition evolution should show the partition shape that actually existed when the data was written. Mixing all specs produced misleading None fields for older partitions.

How was this tested?

• make lint
• uv run python -m pytest tests/io/test_pyarrow.py -k "partition_evolution" -v
• CI: full integration suite (GitHub Actions)

Closes #1120

[kevinjqliu]

LGTM! Thanks!

[kevinjqliu]

Thanks for the PR @010Soham