chore!: Remove active references from SnapController

[Mrtenz]

This removes activeReferences from the Snap runtime data, including the methods to increment and decrement it. This was never used in production.

---

Note

Medium Risk
Removes public SnapController APIs (incrementActiveReferences/decrementActiveReferences) and drops the activeReferences runtime guard, which could change idle-time termination behavior for any downstream code that relied on keeping snaps alive.

Overview
Removes activeReferences tracking from SnapController runtime data, including deleting the incrementActiveReferences/decrementActiveReferences methods and the associated idle-timeout exclusion.

Updates tests by removing the scenario that asserted snaps with open sessions are not terminated, and documents the breaking removal in the snaps-controllers changelog.

^{Written by Cursor Bugbot for commit f4474b4. This will update automatically on new commits. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (controller-refactors@75f65f4). Learn more about missing BASE report.

Additional details and impacted files

@@                   Coverage Diff                   @@
##             controller-refactors    #3920   +/-   ##
=======================================================
  Coverage                        ?   98.56%           
=======================================================
  Files                           ?      425           
  Lines                           ?    12315           
  Branches                        ?     1934           
=======================================================
  Hits                            ?    12138           
  Misses                          ?      177           
  Partials                        ?        0           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.