chore: test-runner and snapshot improvements

[DylanPiercey]

Description

Pulls some test runner and snapshot improvements from the WIP lazy load branch.

• Unify ssr/csr test fixture step execution
• Extract html/bundle size stats into size.json files
• Improve browser vm script execution and waiting
• Other minor cleanups

[changeset-bot]

⚠️ No Changeset found

Latest commit: 31a2210

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.78%. Comparing base (f7b067e) to head (31a2210).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3204   +/-   ##
=======================================
  Coverage   92.78%   92.78%           
=======================================
  Files         372      372           
  Lines       47322    47322           
  Branches     3387     3387           
=======================================
  Hits        43909    43909           
  Misses       3380     3380           
  Partials       33       33           

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[coderabbitai]

Caution

Review failed

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Walkthrough

This PR refactors the Marko runtime initialization and resumption mechanism, replacing a single-runtime ID caching scheme with a multi-render cache (curRenders), introduces new async placeholder management helpers, adds a lazy template loading subsystem, reorders scheduler frame coordination, and creates 119+ test fixture files defining size metric expectations for bundle compression validation across interop and main test directories.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main changes: test runner improvements, snapshot handling, and test infrastructure enhancements reflected throughout the changeset.
Description check	✅ Passed	The description is directly related to the changeset, explaining the extraction of size statistics into size.json files, test runner unification, and VM improvements that are evident in the changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch test-runner-improvements

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