[wrangler] Fix relative imports from nested entry points when using base_dir

[devin-ai-integration]

Fixes #6353.

When using base_dir with no_bundle = true and a nested entry point (e.g., main = "./some/base_dir/nested/index.js" with base_dir = "./some/base_dir"), relative imports like ../foo.js would fail with "internal error" because Miniflare's modulesRoot was incorrectly set to the entry point's directory instead of the configured base_dir.

The fix conditionally sets modulesRoot in buildSourceOptions():

• When the script path is within entry.moduleRoot (e.g., no_bundle with base_dir), use entry.moduleRoot
• Otherwise, fall back to path.dirname(scriptPath) (e.g., bundled output in temp directory)

This conditional approach ensures the fix only applies to the no_bundle case and doesn't break normal bundling where the output is in a temp directory outside moduleRoot.

Key review points:

• The entry.moduleRoot is already computed correctly in entry.ts (line 160-161) based on base_dir or defaults to path.dirname(entry.file), so this change should be safe for workers without base_dir
• The new test simulates the exact scenario from the issue: nested entry point importing a module from the parent directory
• The existing "should start Miniflare with module worker" test was updated to have module names consistent with moduleRoot (e.g., name: "esm/add.cjs" with filePath: "/virtual/esm/add.cjs" instead of inconsistent paths)

Human review checklist:

• Verify entry.moduleRoot is always correctly populated in all code paths
• Confirm the conditional path prefix check handles edge cases (e.g., similar path prefixes, Windows vs Unix separators)
• Confirm the existing test updates don't mask any regressions (the old test had inconsistent module name/filePath which happened to work with the old path.dirname(scriptPath) behavior)

---

• Tests
  • Tests included/updated
  • Automated tests not possible - manual testing has been completed as follows:
  • Additional testing not necessary because:
• Public documentation
  • Cloudflare docs PR(s):
  • Documentation not necessary because: This is a bug fix for existing functionality

Devin PR requested by lrapoport@cloudflare.com

Link to Devin run: https://app.devin.ai/sessions/47e122404e334bb19ec20b6e19efedb5

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commit: d818b6d