[spark] Record the write operation type in snapshot properties

[Zouxxyy]

Purpose

A Paimon snapshot only records the physical CommitKind (APPEND/COMPACT/OVERWRITE/...), not the logical operation that produced it — so an APPEND from INSERT INTO cannot be told apart from one produced by MERGE INTO.

This PR records the logical operation type in the snapshot properties map under the key operation. No format change — Snapshot already has a properties: Map<String, String> field.

Core: add InnerTableCommit#withCommitProperties(...), applied in TableCommitImpl so the properties land on every snapshot the commit generates (both the append and overwrite paths, since FileStoreCommitImpl sources snapshot properties from committable.properties()).

Spark (both v1 and v2 write paths):

SQL	operation
INSERT INTO	WRITE
INSERT OVERWRITE	OVERWRITE
DELETE	DELETE
UPDATE	UPDATE
MERGE INTO	MERGE
CREATE TABLE AS SELECT	CREATE TABLE AS SELECT
(CREATE OR) REPLACE TABLE AS SELECT	REPLACE TABLE AS SELECT / CREATE OR REPLACE TABLE AS SELECT

Tests

Added SnapshotOperationTest (paimon-spark-ut) asserting the recorded operation for INSERT/OVERWRITE/UPDATE/DELETE/MERGE under both spark.paimon.write.use-v2-write=true and false, plus CTAS/RTAS.

[JingsongLi]

[P2] BatchTableCommit is annotated @Public, so adding a new abstract method breaks existing third-party implementations at compile time (and can surface as AbstractMethodError for already-compiled implementations). Since this extension is optional for older implementations, could we make it a Java 8 default method and keep the concrete override in TableCommitImpl?

[JingsongLi]

[P2] This only covers row-rewrite deletes. Metadata-only deletes are optimized before this command runs (for example DELETE FROM t or a partition-only DELETE becomes TruncatePaimonTableWithFilterExec), and that path calls truncateTable / truncatePartitions without any snapshot properties. Those DELETE snapshots would still miss operation=DELETE, so we need to carry SnapshotOperation.DELETE through the truncate path as well.