fix: Skip refetching the registry in handleRegistryUpdate

[FrederikBolding]

Our tests didn't catch this, but in production, triggering SnapRegistryController:registryUpdated triggers handleRegistryUpdate which may try to refetch the registry and cause an infinite loop. We can fix this by passing a flag to not refetch the registry.

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Note

Medium Risk
Changes registry verification/version-resolution calls to optionally skip refetching, which could alter behavior on allowlist misses and impact snap blocking/auto-update flows if misused.

Overview
Prevents an infinite update loop when handling SnapRegistryController:registryUpdated by ensuring SnapController#handleRegistryUpdate does not trigger a registry refetch during blocklist checks and preinstalled allowlist version resolution.

This adds a skipRefetch flag plumbed through SnapRegistryController:get and SnapController#resolveAllowlistVersion (forwarded to SnapRegistryController:resolveVersion), and updates the corresponding SnapController test to assert the new get(..., true) call signature.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.55%. Comparing base (22f8da9) to head (c0401da).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3961      +/-   ##
==========================================
- Coverage   98.56%   98.55%   -0.01%     
==========================================
  Files         428      428              
  Lines       12347    12349       +2     
  Branches     1940     1942       +2     
==========================================
+ Hits        12170    12171       +1     
- Misses        177      178       +1     

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