Fix flaky PARTIAL/FINAL plan assertion in rateFunctionsNormalTest

[JackieTien97]

Description

IoTDBTableAggregation2IT.rateFunctionsNormalTest (inherited from IoTDBTableAggregationIT) fails sporadically:

Expected a PARTIAL aggregation in plan: { ... "Step": "SINGLE" ... "RegionId": "3", "DeviceNumber": "8" ... }

Root cause

assertRateQueryUsesIntermediateAggregation unconditionally requires the EXPLAIN (FORMAT JSON) output of an ungrouped rate()/increase()/irate()/delta() query over rate_merge_test to contain a PARTIAL/FINAL two-step aggregation. That split only exists when the scanned data spans more than one DataRegion.

IoTDBTableAggregation2IT runs with data_partition_allocation_strategy = SHUFFLE. PartitionBalancer.shuffleAllocationStrategy assigns each (seriesSlot, timeSlot) to a random DataRegionGroup, and all 8 rows of rate_merge_test fall into one time partition. So occasionally all 8 devices land in the same DataRegion; the planner then correctly produces a SINGLE-step aggregation with one DeviceTableScanNode, and the assertion fails even though both the plan and the query result are correct (the result comparison right before the assertion had already passed).

Fix

Count the distinct RegionId values in the JSON plan first. Skip the PARTIAL/FINAL check when the plan scans fewer than two distinct regions (a SINGLE aggregation is the correct plan there), and keep asserting it whenever the data actually spans multiple regions — which preserves the original intent of the check in the deterministic base-class environment (CUSTOM extension policy with 2 DataRegions per DataNode).

Verification

• IoTDBTableAggregationIT#rateFunctionsNormalTest and IoTDBTableAggregation2IT#rateFunctionsNormalTest pass locally (TableSimpleIT).
• The region-count regex was verified against the single-region failing plan shape (count 1 → skip), a multi-region shape (count 2 → assert), and "RegionId": "Not Assigned" (count 0 → skip).

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 42.33%. Comparing base (7a38e7e) to head (1e54da9).

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #18556      +/-   ##
============================================
- Coverage     42.34%   42.33%   -0.01%     
  Complexity      413      413              
============================================
  Files          5411     5411              
  Lines        390231   390231              
  Branches      51071    51071              
============================================
- Hits         165233   165221      -12     
- Misses       224998   225010      +12     

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