Enhance error handling in device editor tunnel by adding detailed error context

[cstns]

Description

Polling for the tunnel status and enabling the editor tunnel is silently failing intermittently when attempting to open the immersive remote instance editor.

This PR is the first, temporary step in gathering more context on the matter by explicitly throwing a custom error that will be caught by our error tracker.

Related Issue(s)

part of #6797

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production
• Link to Changelog Entry PR, or note why one is not needed.

Labels

• Includes a DB migration? -> add the area:migration label

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.60%. Comparing base (c86841d) to head (0a9e69d).
⚠️ Report is 7 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6798   +/-   ##
=======================================
  Coverage   76.60%   76.60%           
=======================================
  Files         398      398           
  Lines       20122    20122           
  Branches     4844     4844           
=======================================
  Hits        15414    15414           
  Misses       4708     4708           

Flag	Coverage Δ
backend	76.60% <ø> (ø)

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