Fix suspension persistence to materialize app state before shutdown save

[ChrisPulman]

What kind of change does this PR introduce?

Fix

What is the current behavior?

Closes #4352

What is the new behavior?

Summary

• Fixes ReactiveUI suspension persistence so ShouldPersistState now forces app state materialization before SaveState runs, covering first-launch shutdown paths and missed launch-signal ordering.
• Adds regression tests for typed and untyped hosts that verify created state, loaded state, and persist-token disposal, including the repro ordering from issue #4352.
• Reviewer context: this addresses the shutdown/disposal failure reproduced in JosiahDanger/SuspensionDisposalBug.

Testing

• dotnet build src\tests\ReactiveUI.Tests\ReactiveUI.Tests.csproj --no-restore
• Ran focused TUnit executables for SuspensionHostExtensionsTests and SuspensionHostExtensionsAotTests on net8.0, net9.0, and net10.0
• Ran a broader SuspensionHost* sweep on net10.0; all passed

What might this PR break?

Checklist

• I have read the Contribute guide
• Tests have been added or updated (for bug fixes / features)
• Docs have been added or updated (for bug fixes / features)
• Changes target the main branch
• PR title follows Conventional Commits

Additional information

[codecov]

Codecov Report

❌ Patch coverage is 81.81818% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.85%. Comparing base (303d184) to head (2c292ab).

Files with missing lines	Patch %	Lines
.../ReactiveUI/Suspension/SuspensionHostExtensions.cs	80.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4353      +/-   ##
==========================================
- Coverage   89.86%   89.85%   -0.02%     
==========================================
  Files         253      253              
  Lines        9652     9659       +7     
  Branches     1476     1481       +5     
==========================================
+ Hits         8674     8679       +5     
  Misses        734      734              
- Partials      244      246       +2     

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