[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.