chore(deps): bump NuGet dependencies and drop EOL net9 MAUI targets

[glennawatson]

What kind of change does this PR introduce?

Build / dependency maintenance:

• Bumps NuGet package versions to latest (verified against nuget.org).
• Drops the end-of-life net9 MAUI target frameworks.

What is the new behavior?

Package bumps

Package	From	To
ReactiveUI.Primitives family	5.8.0	6.0.0
DynamicData	9.4.31	9.4.33
TUnit / TUnit.Core	1.57.0	1.58.0
SonarAnalyzer.CSharp	10.27.0.140913	10.28.0.143324
Microsoft.CodeAnalysis.Analyzers	5.3.0	5.6.0
Microsoft.CodeAnalysis.CSharp.Workspaces	5.3.0	5.6.0
Microsoft.CodeAnalysis.PublicApiAnalyzers	5.0.0-1.25277.114	5.6.0

MAUI net9 targets removed

• The net9 MAUI heads (plain net9.0, and Android/Apple) are dropped; MAUI now builds net10+ only.
• Per the .NET MAUI support policy, .NET 9 MAUI reached end of support on 12 May 2026: https://dotnet.microsoft.com/en-us/platform/support/policy/maui
• The dead net9 MauiVersion pin (9.0.120) was removed from central package management.

What is the current behavior?

• Package versions were one or more releases behind latest on the packages listed above.
• The MAUI projects (ReactiveUI.Maui, ReactiveUI.Maui.Reactive) and their test projects still multi-targeted a net9 MAUI head that is now out of support.

What might this PR break?

• Consumers building the ReactiveUI.Maui packages against net9 MAUI must move to net10+. .NET 9 MAUI is already out of support (12 May 2026), so this only removes an unsupported target.
• Windows / WinUI3 targets are unaffected: the net9-windows target frameworks remain in place (WinUI3 is not part of the MAUI net9 removal).
• Android MAUI (net10/net11) and Apple MAUI (net10/net11) were already free of net9 and are unchanged.
• ReactiveUI.Primitives 6.0.0 is a major bump; core library builds clean and the full ReactiveUI.Tests suite passes on net10.0 (1966 tests, 0 failures).

Checklist

• I have read the Contribute guide
• Tests have been added or updated (not applicable; dependency and targeting maintenance)
• Docs have been added or updated (not applicable)
• Changes target the main branch
• PR title follows Conventional Commits

Additional information

• Framework-aligned bands were already at their latest per-TFM patch and are unchanged: MAUI net10 (10.0.80) / net11 preview, ASP.NET Core (net8 8.0.28 / net9 9.0.17 / net10 10.0.9 / netstandard 3.1.32), and System.Text.Json / System.Collections.Immutable / Microsoft.Extensions.DependencyModel / Microsoft.Data.Sqlite.Core at 10.0.9.
• Deliberately stayed on the stable channel where only newer prereleases exist: System.Reactive and Microsoft.Reactive.Testing (7.0-rc), MinVer (8.0-rc), Microsoft.SourceLink.GitHub (11.0-preview), bunit (2.8-preview), BenchmarkDotNet (0.16-preview), and Microsoft.Windows.CsWinRT (already on a 2.3.0 prerelease pin; the 3.0-preview major was not adopted).
• Verification (Linux, net10.0): core ReactiveUI builds with 0 warnings; ReactiveUI.Tests builds with 0 warnings and all 1966 tests pass. Windows-only TFMs are validated by CI.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.06%. Comparing base (c9e11d4) to head (66192ba).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4391      +/-   ##
==========================================
+ Coverage   93.05%   93.06%   +0.01%     
==========================================
  Files         339      339              
  Lines       14882    14882              
  Branches     1567     1567              
==========================================
+ Hits        13848    13850       +2     
+ Misses        770      767       -3     
- Partials      264      265       +1     

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud