Admit object spread computed property keys

[rogeralsing]

Summary

• allow supported object literal spans, including spread-only object literals, as computed property key payloads
• thread string constants through computed property key span compilation so object literal keys can emit safely
• replace the old readComputedSpreadKey fallback assertion with production fast-path coverage

Verification

• rtk dotnet test tests/Asynkron.JsEngine.Tests -c Release --filter 'FullyQualifiedNameUnifiedBytecodeProductionEligibilityTests.Evaluate_PropertyReadAdjacentFamilies_DeclineWithExplicitCodes|FullyQualifiedNameUnifiedBytecodeProductionInvocationTests.ComputedPropertyReadWithSpreadObjectKey_UsesUnifiedBytecodeProductionFastPath|FullyQualifiedNameUnifiedBytecodeProductionInvocationTests.ObjectLiteralSpread_UsesUnifiedBytecodeProductionFastPathAndCopiesSymbolKeys|FullyQualifiedNameUnifiedBytecodeProductionInvocationTests.ObjectLiteralConstruction_UsesUnifiedBytecodeProductionFastPathAndCoercesComputedKeys|FullyQualifiedNameUnifiedBytecodeProductionInvocationTests.ComputedPropertyReadWithOrdinaryDynamicKey_UsesUnifiedBytecodeProductionFastPath'\n- rtk dotnet test tests/Asynkron.JsEngine.Tests -c Release --filter 'FullyQualifiedNameUnifiedBytecodeProductionEligibilityTests|FullyQualifiedNameUnifiedBytecodeProductionInvocationTests|FullyQualifiedNameUnifiedBytecodeProductionSpreadCallTests|FullyQualifiedNameUnifiedBytecodeProductionConstructCallTests|FullyQualifiedNameExpressionProgramLoweringTests|FullyQualifiedNameExpressionProgramCoverageMapTests|FullyQualifiedNameAstFreeExecutionAssertionTests'\n- rtk dotnet build src/Asynkron.JsEngine/Asynkron.JsEngine.csproj -c Release\n- rtk rg "EvaluateExpression\\(|ProfileEvaluateExpression\\(" src/Asynkron.JsEngine/Ast/TypedAstEvaluator.ExecutionPlanRunner*\n- rtk git diff --check

[Copilot]

Pull request overview

This PR expands unified-bytecode production support for computed property keys by allowing certain object literal spans (including object spreads) to be compiled as part of the computed-key “payload”, and ensures the unified-bytecode compiler correctly threads string constants so object literal property names can be emitted safely in that context.

Changes:

• Allow admitted simple object-literal spans (including spread-only) inside computed property key spans for production eligibility and compilation.
• Thread stringConstants through computed property key span compilation and stage/commit string constants in boundary compilation paths that can now emit object literals.
• Update tests to validate the unified-bytecode production fast-path is used (instead of asserting fallback) and adjust eligibility expectations accordingly.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
tests/Asynkron.JsEngine.Tests/UnifiedBytecodeProductionInvocationTests.cs	Replaces a fallback-based test with a fast-path assertion for computed keys that use spread-only object literals.
tests/Asynkron.JsEngine.Tests/UnifiedBytecodeProductionEligibilityTests.cs	Updates expected decline code to reflect new eligibility and improves assertion diagnostics.
src/Asynkron.JsEngine/Execution/UnifiedBytecode/UnifiedBytecodeProductionEligibility.cs	Relaxes eligibility rules to admit object spreads in computed-key payloads when they’re part of admitted object literal spans; adds support for CreateObject in computed-key span measurement.
src/Asynkron.JsEngine/Execution/UnifiedBytecode/UnifiedBytecodeCompiler.cs	Extends computed property key span compilation to emit simple object literal spans (including spreads) and stages/threads string constants so object literal property names are correctly recorded.

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