Drop official support for .NET Framework

[Tyrrrz]

Supporting .NET Framework in CliWrap has started taking up too much effort. Considering that .NET Framework is legacy technology at this point and .NET (Core) is pretty much as mature as it gets (having been out for 9+ years), I see no reason to justify the effort to maintain official support for .NET Framework in this library.

Users can still continue to use CliWrap with .NET Framework, however they will need to figure out any run-time compatibility issues themselves. CliWrap will continue targeting .NET Standard 2.0 which should ensure compatibility with .NET Framework on paper (and, as experience shows, only on paper).

This PR removes tests running against .NET Fx and updates package references that previously caused compatibility issues. It also removes a framework reference on System.Management.

[Copilot]

Pull Request Overview

This PR drops official support for .NET Framework by removing related tests and updating package references.

• Removed .NET Framework-specific tests and references.
• Updated package reference conditions using the new shorthand.
• Adjusted the condition for the System.Management package reference to reflect the new support policy.

Reviewed Changes

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

File	Description
Directory.Build.props	Updated condition syntax for nullability annotations.
CliWrap/CliWrap.csproj	Upgraded package versions and revised MSBuild conditions.
CliWrap.Tests/CliWrap.Tests.csproj	Removed .NET Framework (net48) target from test suites.
CliWrap.Tests.Dummy/CliWrap.Tests.Dummy.csproj	Simplified target framework configuration by removing net48 support.

Comments suppressed due to low confidence (1)

CliWrap/CliWrap.csproj:43

• Verify that the updated condition for including the System.Management package accurately reflects the intended framework targets without inadvertently excluding other desired frameworks.

Condition="!$([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)', 'netcoreapp3.0'))"

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.69%. Comparing base (e66b1c6) to head (d602cb2).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #296      +/-   ##
==========================================
+ Coverage   88.81%   94.69%   +5.88%     
==========================================
  Files          48       48              
  Lines        1207     1207              
  Branches       95       95              
==========================================
+ Hits         1072     1143      +71     
+ Misses        109       38      -71     
  Partials       26       26              

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