Prove discarded call unified bytecode routing

[rogeralsing]

Summary

• add eligibility and public route proof that a discarded identifier call compiles to the production unified bytecode call boundary and final Pop
• document that there is no retained discard-specific production decline; remaining discarded-expression declines belong to their underlying semantic family
• add a drift guard against reintroducing stale blanket non-directive discard-decline wording

Verification

• rtk dotnet test tests/Asynkron.JsEngine.Tests -c Release --filter "FullyQualifiedNameUnifiedBytecodeProductionEligibilityTests.Evaluate_DiscardedIdentifierCallCandidate_AcceptsInvocationBoundaryAndPop|FullyQualifiedNameUnifiedBytecodeProductionInvocationTests.DiscardedIdentifierCall_UsesUnifiedBytecodeProductionFastPathAndKeepsSideEffects|FullyQualifiedName~ExpressionProgramCoverageMapTests.UnifiedBytecodeDiscardDocumentation_DoesNotPreserveStaleBlanketDeclineRule"
• rtk dotnet test tests/Asynkron.JsEngine.Tests -c Release --filter "FullyQualifiedNameUnifiedBytecodeProductionEligibilityTests|FullyQualifiedNameUnifiedBytecodeProductionInvocationTests|FullyQualifiedName~ExpressionProgramCoverageMapTests"
• rtk dotnet build src/Asynkron.JsEngine/Asynkron.JsEngine.csproj -c Release
• rtk rg "EvaluateExpression(|ProfileEvaluateExpression(" src/Asynkron.JsEngine/Ast/TypedAstEvaluator.ExecutionPlanRunner*
• rtk git diff --check

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