Improve metadata OOM diagnostics

[Caideyipi]

Description

This PR improves metadata/query-analysis OOM diagnostics when result-set column expansion or schema fetch runs out of memory.

Changes:

• Track matched, expanded, generated, and schema-fetch deserialized result columns in MPPQueryContext.
• Enrich MemoryNotEnoughException during metadata analysis with column counts, SLIMIT/SOFFSET, ALIGN BY DEVICE guidance, memory shortage, and estimated exceeded columns.
• Record column counts during expression expansion and schema fetch batch deserialization.
• Add MPPQueryContextTest coverage for enriched result-column and schema-fetch OOM messages, plus the no-context fallback path.

Verification

• mvn spotless:apply -pl iotdb-core/datanode
• git diff --check
• mvn "-Ddevelocity.off=true" test -pl iotdb-core/datanode -Dtest=MPPQueryContextTest currently fails before running tests during datanode main-source compilation because of pre-existing/unrelated missing symbols in AstBuilder, DataNodeMemoryConfig, TableConfigTaskVisitor, DatasetHeaderFactory, ShowCreate*Task, and DataRegionConsensusImpl.

[codecov]

Codecov Report

❌ Patch coverage is 77.15736% with 45 lines in your changes missing coverage. Please review.
✅ Project coverage is 41.70%. Comparing base (7f41f06) to head (9fa3066).
⚠️ Report is 32 commits behind head on master.

Files with missing lines	Patch %	Lines
...e/iotdb/db/queryengine/common/MPPQueryContext.java	78.53%	38 Missing ⚠️
...lan/analyze/schema/ClusterSchemaFetchExecutor.java	0.00%	6 Missing ⚠️
...eryengine/common/schematree/ClusterSchemaTree.java	75.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #18039      +/-   ##
============================================
+ Coverage     41.42%   41.70%   +0.27%     
  Complexity      318      318              
============================================
  Files          5282     5296      +14     
  Lines        369246   372014    +2768     
  Branches      47786    48128     +342     
============================================
+ Hits         152978   155165    +2187     
- Misses       216268   216849     +581     

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[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud