Snapshot: Make manifest-list required

[Fokko]

Since we don't support manifests, we can assume that the manifest-list is there all the time.

[kevinjqliu]

we can assume that the manifest-list is there all the time.

what about for V1 tables where the manifest-list field is optional?

[Fokko]

Then we should read the manifests field, but that has never been implemented on PyIceberg. No engine is using that, and I think we should deprecate it. By making the manifest-list optional, we error explicitly when we try to load a snapshot that relies on the manifests field.

[kevinjqliu]

LGTM

[kevinjqliu]

looks like manifest-list is missing in our example

iceberg-python/tests/conftest.py

Line 628 in b0ea716

"snapshots": [{"snapshot-id": 1925, "timestamp-ms": 1602638573822}],

[kevinjqliu]

tests/table/test_metadata.py::test_serialize_v1 and tests/table/test_metadata.py::test_v1_write_metadata_for_v2 also fails

[Fokko]

@kevinjqliu Thanks, some bad tests. They didn't have the manifest-list in the snapshot, which is invalid according to the spec.