[FLINK-40477][table] Fix constraint enforcer for partial deletes

[fhueske]

What is the purpose of the change

The sink NOT NULL enforcer inspected every row regardless of RowKind, so a by-key (partial) delete tombstone (whose non-key columns are legitimately null) was rejected (ERROR) or silently dropped (DROP), losing the delete.

This PR relaxes NOT NULL for the non-key columns of DELETE rows in key-only-delete pipelines; key columns and all other row kinds stay enforced.

Brief change log

• pass information about partial deletes and PK to constraint checker
• skip null checks of non-key, non-null declared columns in DELETE change records
• add tests to validate correctness

Verifying this change

• Added semantic tests asserting correct skipping of checks

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): yes
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? na
• If yes, how is the feature documented? n/a

---

Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

Generated-by: Claude Code (Opus 4.8, 1M)

[flinkbot]

CI report:

• 024400b Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build