Admit optional computed reads after named prefixes

[rogeralsing]

Summary

• admit prefixed optional computed reads like box.child?.[key] into production unified bytecode
• emit named receiver prefixes before the nullish boundary, then computed key/property reads and short-circuit suffixes
• update the unified bytecode expansion contract and add eligibility/invocation coverage

Verification

• rtk dotnet test tests/Asynkron.JsEngine.Tests -c Release --filter "FullyQualifiedNameUnifiedBytecodeProductionEligibilityTests.Evaluate_OptionalComputedPropertyReadWithNamedPrefix_AcceptsWithJumpIfNullishReplaceUndefinedOpcode|FullyQualifiedNameUnifiedBytecodeProductionInvocationTests.OptionalComputedPropertyReadAfterNamedPrefix_SkipsKeyOnNullish|FullyQualifiedNameUnifiedBytecodeProductionInvocationTests.OptionalComputedPropertyRead_ReturnsPropertyValueWhenBaseIsNonNull|FullyQualifiedNameUnifiedBytecodeProductionInvocationTests.OptionalComputedPropertyRead_ReturnsUndefinedWhenBaseIsNull"
• rtk dotnet test tests/Asynkron.JsEngine.Tests -c Release --filter "FullyQualifiedNameUnifiedBytecodeProductionEligibilityTests|FullyQualifiedNameExpressionProgramCoverageMapTests.UnifiedBytecodeExpansionContract_ListsRequiredHeadingsAndCurrentEnums|FullyQualifiedName~UnifiedBytecodeProductionInvocationTests"
• rtk dotnet build src/Asynkron.JsEngine/Asynkron.JsEngine.csproj -c Release
• rtk git diff --check
• rtk rg "EvaluateExpression(|ProfileEvaluateExpression(" src/Asynkron.JsEngine/Ast/TypedAstEvaluator.ExecutionPlanRunner*
• rtk ./tools/profile forloop --memory

Notes

• Full tests are currently blocked by the same 14 baseline failures reproduced on untouched main in the TDZ/const/slot/tail-call subset, so they are not introduced by this branch.
• rtk dotnet format is a verify wrapper and reported pre-existing analyzer findings in these large touched compiler files; local whitespace issues from this change were fixed.

[Copilot]

Copilot encountered an error and was unable to review this pull request. You can try again by re-requesting a review.