partial-update: support ignore-delete semantics

[shyjsarah]

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• I searched the existing issues and pull requests and found nothing similar.

Please describe the bug

Paimon Rust currently rejects ignore-delete options on primary-key tables using
merge-engine=partial-update, even though Java Paimon supports this mode.

For example, creating or opening a table with either option fails validation:

merge-engine=partial-update
ignore-delete=true

or:

merge-engine=partial-update
partial-update.ignore-delete=true

The read-side and flush-time partial-update merge functions also reject
DELETE and UPDATE_BEFORE rows unconditionally. This prevents Rust readers
from opening Java-created tables and historical files that use the supported
ignore-delete semantics.

Expected behavior:

• Both ignore-delete and partial-update.ignore-delete are accepted.
• With an effective value of true, DELETE and UPDATE_BEFORE are ignored.
• The default and an explicit false still reject retract rows.
• Ignored retract rows do not consume writer buffer, sequence numbers, or enter
  input changelog files.
• Once enabled, the effective value cannot be changed from true to false,
  matching Java Paimon compatibility safeguards.
• Other advanced partial-update options remain unsupported.

Proposed solution

• Narrowly allowlist the two supported option keys in partial-update validation.
• Apply ignore-delete semantics in both read-side merge and write-side filtering.
• Filter direct _VALUE_KIND batches before writer buffering.
• Add schema, writer, reader, core integration, and DataFusion integration tests.
• Document the supported behavior and remaining limitations.

Are you willing to submit a PR?

• I'm willing to submit a PR!