Core: add labels to the load table/view read path - #18045

Parse the optional `labels` field of the REST load-table response and
expose it through Table::labels(), mirroring apache/iceberg#18045 and
live on the Table instance instead of TableMetadata.

Part of apache#938.

Parse the optional `labels` field of the REST load-table response and
expose it through Table::labels(), mirroring apache/iceberg#18045 and
apache/iceberg#18046. Labels are catalog-provided rather than table
state, so they live on the Table instance instead of TableMetadata.

Part of apache#938.

Parse the optional `labels` field of the REST load-table response and
expose it through Table::labels(), mirroring apache/iceberg#18045 and
apache/iceberg#18046. Labels are catalog-provided rather than table
state, so they live on the Table instance instead of TableMetadata.

Part of apache#938.

Parse the optional `labels` field of the REST load-table response and
expose it through Table::labels(), mirroring apache/iceberg#18045 and
apache/iceberg#18046. Labels are catalog-provided rather than table
state, so they live on the Table instance instead of TableMetadata.

Part of #938.

…he#4320)

* Parse catalog labels in REST load table and load view responses

The REST spec adds an optional `labels` field to LoadTableResult and
LoadViewResult for catalog-provided enrichment such as ownership or
classification. PyIceberg dropped the field. Add `Labels` and
`FieldLabel` models and parse `labels` on `TableResponse` and
`ViewResponse`, matching the Java read path (apache/iceberg#18045).

* Read non-object labels as empty

A string, list, number, or bool `labels` value failed the whole load.
Java `LabelsParser` reads keys only under `hasNonNull`, so it returns
empty labels for any non-object value. Do the same.

* Parse catalog labels in REST load table and load view responses

The REST spec adds an optional `labels` field to LoadTableResult and
LoadViewResult for catalog-provided enrichment such as ownership or
classification. PyIceberg dropped the field. Add `Labels` and
`FieldLabel` models and parse `labels` on `TableResponse` and
`ViewResponse`, matching the Java read path (apache/iceberg#18045).

* Read non-object labels as empty

A string, list, number, or bool `labels` value failed the whole load.
Java `LabelsParser` reads keys only under `hasNonNull`, so it returns
empty labels for any non-object value. Do the same.

* Expose catalog labels on Table

Labels parsed from the load response were not reachable from the
loaded table. Add `Table.labels`. The REST catalog sets it on load,
create, and register. Other catalogs and staged tables
(`create_table_transaction`) get empty labels. Labels are not table
state: they are not part of equality, and refresh and commits keep
them. This matches the Java `SupportsLabels` behavior
(apache/iceberg#18046).

* Test labels on create, register, and pickle

Create and register hand labels to the same `_response_to_table` as
load, but only load was tested. Check all three. Also pin that a
pickled table keeps its labels, the one intended difference from Java,
where `BaseTable.labels` is transient.

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Co-authored-by: Fokko Driesprong <[email protected]>