Admit optional computed spread calls

[rogeralsing]

Summary

• admit optional-start computed member spread calls such as a?.boxkey
• use the existing spread-mask call boundary for the optional computed call path
• update the production eligibility/runtime proofs and bytecode expansion contract

Tests

• rtk dotnet test tests/Asynkron.JsEngine.Tests -c Release --filter "FullyQualifiedNameUnifiedBytecodeProductionEligibilityTests.Evaluate_OptionalChainComputedPlainSpreadCallExpressionPlan_AcceptsExecutableInvocationBoundary|FullyQualifiedNameUnifiedBytecodeProductionInvocationTests.OptionalChainComputedPlainSpreadCall_UsesUnifiedBytecodeProductionFastPath|FullyQualifiedNameUnifiedBytecodeProductionSpreadCallTests|FullyQualifiedNameExpressionProgramLoweringTests.ReturnInstruction_SpreadCallExpression_IsLoweredToExpressionProgram|FullyQualifiedName~ExpressionProgramCoverageMapTests.UnifiedBytecodeExpansionContract_ListsRequiredHeadingsAndCurrentEnums"
• rtk dotnet test tests/Asynkron.JsEngine.Tests -c Release --filter "FullyQualifiedNameUnifiedBytecodeProductionEligibilityTests|FullyQualifiedNameUnifiedBytecodeProductionInvocationTests|FullyQualifiedNameUnifiedBytecodeProductionSpreadCallTests|FullyQualifiedNameExpressionProgramLoweringTests|FullyQualifiedNameExpressionProgramCoverageMapTests|FullyQualifiedNameAstFreeExecutionAssertionTests"
• 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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