feat: support TC39 import defer proposal

[bartlomieju]

Summary

• Adds support for the TC39 "Deferred Module Evaluation" proposal
• Enables V8 --js-defer-import-eval flag
• Separates ModuleImportPhase::Defer handling from Evaluation phase in module loading
• Integration test validates deferred evaluation semantics

Background

The import defer proposal (Stage 3) allows loading modules without immediate execution:

import defer * as ns from "./module.js";
// Module is loaded but NOT executed
console.log(ns.value); // Module executes here, on first property access

Changes

File	Change
core/runtime/setup.rs	Add --js-defer-import-eval V8 flag
core/modules/map.rs	Separate Defer phase handling (instantiate without evaluate)
testing/lib.rs	Add import_defer integration test
testing/integration/import_defer/*	Test files + implementation notes

Test plan

• All existing tests pass (cargo test -p deno_core_testing - 55 tests)
• import_defer test passes with V8 14.6 (rusty_v8 146) runtime support

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.61%. Comparing base (0c7f83e) to head (8c7e545).
⚠️ Report is 437 commits behind head on main.

Files with missing lines	Patch %	Lines
core/modules/map.rs	0.00%	20 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1280      +/-   ##
==========================================
- Coverage   81.43%   77.61%   -3.82%     
==========================================
  Files          97      105       +8     
  Lines       23877    26813    +2936     
==========================================
+ Hits        19445    20812    +1367     
- Misses       4432     6001    +1569     

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[bartlomieju]

Closing in favor of denoland/deno#32360