[spark] Introduce reassign_row_id procedure

[zhuxiangyi]

Purpose

Flink provides reassign_row_id both as an action (ReassignRowIdAction) and as a
procedure, but Spark has no counterpart. As a result, users running Paimon on Spark
cannot make row IDs of a data evolution table partition-contiguous.

Row IDs are assigned in commit order, so writes that interleave across partitions
leave each partition with a scattered row-id range, which hurts column-store read
efficiency. Reassignment rewrites the row-id ranges so that each partition owns a
contiguous block.

This PR adds the Spark procedure:

-- reassign all partitions
CALL sys.reassign_row_id(table => 'default.T')

-- reassign selected partitions ("," means AND, ";" means OR)
CALL sys.reassign_row_id(table => 'default.T', partitions => 'dt=2026-05-19')

Notes on the implementation:

• The actual work is delegated to DataEvolutionRowIdReassigner in paimon-core,
  which is engine-agnostic and already used by the Flink side, so no reassignment
  logic is duplicated here.
• partitions is parsed with the existing
  SparkProcedureUtils#convertPartitionsToPartitionPredicate, keeping the partition
  spec syntax consistent with other Spark procedures; when omitted, all partitions
  are reassigned.
• The table must have row-tracking.enabled = true and data-evolution.enabled = true;
  both are validated by the core reassigner.
• The procedure returns a single result string describing whether the reassignment
  happened, and for a skip, why it was skipped.

Docs for the new procedure are added to docs/docs/spark/procedures.md.

Tests

Added ReassignRowIdProcedureTest in paimon-spark-ut, covering:

• reassigning a table written with interleaved partitions, asserting the row IDs
  become contiguous per partition and the data itself is unchanged;
• idempotency: a second call on already-contiguous row IDs is skipped;
• the partitions filter, for both a spec that matches no partition (skipped) and
  one that matches (reassigned);
• the two precondition failures, row-tracking.enabled=true and
  data-evolution.enabled=true;
• a non-partitioned table, which is skipped.

[JingsongLi]

+1