Admit binary template substitutions in call args

[rogeralsing]

Summary

• admit simple binary substitutions inside untagged template literal call arguments for production unified bytecode routing
• add an eligibility proof and runtime route-hit proof for the logExpr template-literal call shape
• update the decline contract CallDependency row to point at a remaining call-dependency decline

Verification

• focused route proof: 5 tests passed
• broad bytecode proof: 888 tests passed
• docs/decline proof: 4 tests passed
• engine build: 2 projects, 0 errors, 0 warnings
• AST seam scan: no EvaluateExpression/ProfileEvaluateExpression hits in execution-plan runner files
• git diff --check: clean

[Copilot]

Pull request overview

This PR widens unified-bytecode production routing to admit a specific previously-declined call-argument shape: untagged template literals whose substitution is a simple binary expression (e.g. `result: ${a + b}`). This fits into the existing “simple template literal span” machinery used by the production eligibility checker and unified-bytecode compiler.

Changes:

• Add coverage proving the unified-bytecode production fast-path is hit for a template literal containing a binary substitution.
• Update production eligibility scanning to recognize the op-sequence for a simple binary substitution inside a template literal span.
• Update the unified-bytecode compiler to emit unified bytecode for that binary-substitution template span and adjust the decline-contract doc row accordingly.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/Asynkron.JsEngine.Tests/UnifiedBytecodeProductionInvocationTests.cs	Adds a runtime/route-hit test proving the fast-path is used for ${a + b} inside an untagged template literal call argument.
tests/Asynkron.JsEngine.Tests/UnifiedBytecodeProductionEligibilityTests.cs	Updates eligibility expectations for the ${a + b} template substitution shape (now accepted) and adds instruction-level assertions.
src/Asynkron.JsEngine/Execution/UnifiedBytecode/UnifiedBytecodeProductionEligibility.cs	Extends “simple template literal span” measurement to include a recognized 5-op binary-substitution sequence.
src/Asynkron.JsEngine/Execution/UnifiedBytecode/UnifiedBytecodeCompiler.cs	Extends template literal span compilation to emit unified bytecode for binary substitutions; introduces a helper for pre-checking operand-load eligibility.
docs/unified-bytecode-expansion-contract.md	Updates the CallDependency row text and proof command to reflect the newly admitted template-literal substitution shape.

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