feat(queryengine): adaptive Plan Cache for table model queries

[Young-Leo]

Description

Introduce an adaptive Plan Cache that caches optimized logical plans for table model queries,
skipping repeated Logical Plan Generation and Logical Optimization for structurally identical SQL.

Core mechanism

• Query fingerprinting: Parameterize literals in SQL and generate an MD5 cache key, so
  SELECT * FROM t WHERE device_id = 'd1' and device_id = 'd2' share the same template.
• Three-state machine per template: MONITOR → ACTIVE → BYPASS. Each template independently
  accumulates EWMA samples before promotion; low-benefit templates are bypassed with a cooldown.
• Safe plan reuse: Only the logical plan is cached. On HIT, literals are re-bound and
  adjustSchema re-resolves devices, time filters, and partition info — Distribution Plan is
  never cached, avoiding stale region/shard topology.
• LRU eviction: LinkedHashMap(accessOrder=true) with dual limits (1000 entries, 64 MB).

Admission control

Transition	Condition
MONITOR → ACTIVE	sampleCount ≥ 5 ∧ ewmaPlanCost ≥ 1 ms ∧ benefitRatio ≥ 30%
MONITOR → BYPASS	sampleCount ≥ 5 ∧ (planCost < 1 ms ∨ benefitRatio < 20%)
ACTIVE → MONITOR	benefitRatio < 30% ∨ planCost < 1 ms (reset & re-evaluate)
BYPASS → MONITOR	cooldown expires (default 10 min)

HIT-path latency tracking: during sustained cache hits, firstResponseLatency is still
recorded and ewmaBenefitRatio is refreshed using historical ewmaReusablePlanningCost,
enabling natural degradation when execution cost grows.

Observability

EXPLAIN ANALYZE VERBOSE outputs Plan Cache diagnostics:
Plan Cache State: ACTIVE
Plan Cache Saved: 5.23 ms
EWMA Reusable Planning Cost: 5.23 ms (threshold: 1.00 ms)
EWMA First Response Latency: 11.80 ms
EWMA Benefit Ratio: 0.4434 (admit: 0.30, bypass: 0.20)
Profile Counters: samples=7, hits=12, misses=0, bypasses=0

Files changed (production)

File	Change
PlanCacheManager.java	New. LRU cache + three-state machine + EWMA evaluation
CachedValue.java	New. Cached plan container with deep-clone and memory estimation
LiteralMarkerReplacer.java	New. AST visitor for literal parameterization
TableNameRewriter.java	New. AST rewriter for table name normalization in cache key
TableLogicalPlanner.java	Integrate cache lookup / write-back / statistics feedback
IoTDBConfig.java / IoTDBDescriptor.java	10 new config properties (smart_plan_cache_*)
MPPQueryContext.java	Bridge planner diagnostics → EXPLAIN ANALYZE output
QueryPlanStatistics.java	New fields for EWMA metrics and profile counters
QueryExecution.java	Record execution time back to PlanCacheManager
FragmentInstanceStatisticsDrawer.java	Render Plan Cache diagnostics in VERBOSE mode
ExplainAnalyzeOperator.java	Pass verbose flag to statistics renderer
Literal.java / StringLiteral / LongLiteral / BinaryLiteral	Add generalizedCopy() for parameterization
SymbolAllocator.java	Expose setNextId() for cached symbol counter restore
PushPredicateIntoTableScan.java	Minor adjustment for cached plan compatibility
ExpressionFormatter.java	Support formatting of parameterized marker literals

Tests

• PlanCacheTest.java — unit tests for state machine transitions and cache eviction