test: pin the multiple-container behaviour behind Func<IHub>

[jamescrosswell]

Description

The hub is registered in DI as Func<IHub> returning () => HubAdapter.Instance, so nothing ever holds a concrete hub. That shape fixed #103 in #157, but nothing in the suite pinned it. This adds regression tests that fail if the registration is "simplified" to a singleton IHub, plus a one-line pointer to #103 at the registration.

• Throwaway container (Sentry.AspNetCore.Tests): with the test server running, a second provider is built from the same services, a hub is resolved from it, and the provider is disposed. An unhandled exception on /throw must still reach the background worker through SentryMiddleware.
• No captured instance (Sentry.Extensions.Logging.Tests): IHub and ISentryClient are resolved, then the SDK's hub is swapped with SentrySdk.UseHub. Captures through both references must reach the new hub.
• Lifetime (Sentry.Extensions.Logging.Tests): after the provider is disposed, SentrySdk still captures. The test also resolves ILoggerFactory, because SentryLoggerProvider.Dispose disposes the hub when it is IDisposable.

Notes for review

• Container ordering differs from the issue's sketch. The issue suggests building the throwaway container before the real one. I checked that order against a simulated regression (singleton IHub holding the initialized hub, Func<IHub> closing over it) and it passes, because the real container's hub simply replaces the throwaway's. The failure only shows when the second container is built after the real one: SentrySdk.UseHub disposes the hub the real container is still holding. The test uses that order.
• All three tests fail against that simulated regression and pass on the current code.
• Lifetime is asserted by behaviour rather than by ServiceDescriptor.Lifetime, since a singleton HubAdapter would be harmless and a descriptor check would reject it.
• The new Extensions.Logging tests swap the global hub, and LoggingTests in the same assembly initializes the SDK concurrently, so they run in a new SentrySdkCollection with DisableParallelization = true (same approach as ProfilingTestCollection).

#skip-changelog

Issues

Closes #5645

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.91%. Comparing base (4af9645) to head (1b89c97).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5646      +/-   ##
==========================================
+ Coverage   74.37%   74.91%   +0.54%     
==========================================
  Files         501      515      +14     
  Lines       18566    18975     +409     
  Branches     3603     3695      +92     
==========================================
+ Hits        13808    14216     +408     
+ Misses       3883     3878       -5     
- Partials      875      881       +6     

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