Admit dynamic load and delete operands

[rogeralsing]

Summary

• admit ordinary dynamic identifier loads through the production unified-bytecode route
• allow ordinary dynamic identifier keys for first-boundary computed property deletes
• add direct route-hit tests for readExternal() and delete box.child[externalKey]
• update stale dynamic/delete contract proof pointers

Verification

• Focused proof: 6 tests passed
• Broad unified-bytecode/lowering pack: 903 tests passed
• Build: 0 errors, 0 warnings
• AST seam scan: no EvaluateExpression/ProfileEvaluateExpression matches
• git diff --check clean

[Copilot]

Pull request overview

This PR widens the production unified-bytecode routing to admit additional “ordinary dynamic” environment operations, specifically dynamic identifier loads and first-boundary computed-property deletes with dynamic identifier keys, and adds regression coverage plus contract documentation updates.

Changes:

• Expanded unified-bytecode eligibility checks to allow first-boundary computed delete obj[key] where key is an ordinary dynamic identifier (when enabled by activation descriptor).
• Updated eligibility and invocation tests to validate the new fast-path/eligibility behavior for dynamic identifier loads and dynamic-key computed deletes.
• Updated the unified-bytecode expansion contract to point to the new/renamed proof tests for dynamic lookup and delete lanes.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
tests/Asynkron.JsEngine.Tests/UnifiedBytecodeProductionInvocationTests.cs	Adds direct fast-path route-hit tests for dynamic identifier reads and dynamic-key computed deletes.
tests/Asynkron.JsEngine.Tests/UnifiedBytecodeProductionEligibilityTests.cs	Updates eligibility assertions to accept ordinary dynamic identifier operations and validates resulting opcodes.
src/Asynkron.JsEngine/Execution/UnifiedBytecode/UnifiedBytecodeProductionEligibility.cs	Threads an “allow ordinary dynamic identifiers” flag into computed-delete candidate checks and computed-key validation.
docs/unified-bytecode-expansion-contract.md	Refreshes proof pointers for the dynamic-lookup and delete lanes reflecting the updated contract.

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