Bugfix: Mitigate external Ubuntu Pro Client issues

[kjohn-msft]

Background: For VMs that are Ubuntu Pro client capable, there are 2 sets of issues that manifest as required security updates not getting installed on machines_ (some machines).

1. Canonical is aware of packages normally seen as updates in the default flow not being shown as required in pro client scans. There is an explanation for this but the way we have taken a tight dependency on pro client when it's functional causes these updates no to get installed.

2. There are cases where wide swathes of security updates are not getting detected by pro client. It was not clear if this was a pro client issue in the past or an issue with our code. The additional code that went in November helped identify that this was a pro client issue when newer reports came in: Apt debstyle882 support, bug-fixes in cache evaluation & manipulation #273

Both problems listed above are being resolved by not fully relying on pro client and using a combined overlay of the default scanning mechanism with whatever pro client reports. This is the 'best of both worlds' approach. Extensive logging additions will help further reviews with Canonical on pro client behaviors without affecting any customer while a multi-stage resolution is ironed out.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.13%. Comparing base (d28c9cc) to head (156b9fa).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #308   +/-   ##
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  Coverage   93.13%   93.13%           
=======================================
  Files         103      103           
  Lines       17555    17566   +11     
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+ Hits        16349    16360   +11     
  Misses       1206     1206           

Flag	Coverage Δ
python27	93.12% <100.00%> (+<0.01%)	⬆️
python312	93.13% <100.00%> (+<0.01%)	⬆️

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[Copilot]

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (3)

src/core/tests/Test_AptitudePackageManager.py:44

• [nitpick] The function name 'mock_linux_distribution_to_return_ubuntu_oracular' may be unclear; consider including the Ubuntu version (e.g., '26') in the name to improve clarity.

def mock_linux_distribution_to_return_ubuntu_oracular(self):

src/core/src/bootstrap/Constants.py:381

• Ensure that updating MAX_OS_MAJOR_VERSION_SUPPORTED to 24 is synchronized with related logic and tests to correctly reflect supported OS versions.

MAX_OS_MAJOR_VERSION_SUPPORTED = 24

src/core/src/package_managers/AptitudePackageManager.py:366

• Consider adding unit tests to fully cover both outcomes of the 'get_security_updates' method and ensure that each branch behaves as expected.

if not ubuntu_pro_client_security_updates_query_success: