daemon, o/i/apparmorprompting: implement ShutDown for InterfacesRequestsManager

[natibek]

Implement ShutDown for the InterfacesRequestsManager to replace the existing shutdown process that uses c.d.tomb.Dying() to signal snapdShuttingDown.

Tracked with: SNAPDENG-36591

[github-actions]

Tue Jun 2 20:17:42 UTC 2026
The following results are from: https://github.com/canonical/snapd/actions/runs/26839655180

Failures:

Preparing:

• openstack:ubuntu-24.04-64:tests/main/nvidia-files:470

Executing:

• openstack:ubuntu-24.04-64:tests/completion/indirect:plain
• openstack:ubuntu-24.04-64:tests/main/refresh-delta

Restoring:

• openstack:ubuntu-24.04-64:tests/completion/indirect:plain
• openstack:ubuntu-24.04-64:tests/completion/
• openstack:ubuntu-24.04-64:
• openstack:ubuntu-24.04-64:tests/main/refresh-delta
• openstack:ubuntu-24.04-64:tests/main/
• openstack:ubuntu-24.04-64:

Skipped tests from snapd-testing-skip

If you wish to have any of the below tests run in your PR, in your PR description, add 'unskip:' followed by a copy-and-pasted list (without variants) of the below tests you wish to run (unskip plus test list must be valid yaml)

• openstack:ubuntu-24.04-64:tests/main/i18n
• openstack:ubuntu-24.04-64:tests/main/snapctl-no-wait

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.07%. Comparing base (bb94da2) to head (4bc5889).
⚠️ Report is 13 commits behind head on master.

Files with missing lines	Patch %	Lines
overlord/ifacestate/apparmorprompting/prompting.go	72.72%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #17147      +/-   ##
==========================================
+ Coverage   79.00%   79.07%   +0.07%     
==========================================
  Files        1379     1380       +1     
  Lines      192453   192506      +53     
  Branches     2464     2466       +2     
==========================================
+ Hits       152043   152224     +181     
+ Misses      31242    31120     -122     
+ Partials     9168     9162       -6     

Flag	Coverage Δ
unittests	79.07% <75.00%> (+0.07%)	⬆️

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