Align conditional compilation directives with target frameworks

[Copilot]

Description

The conditional PropertyGroup for ImplicitUsings referenced frameworks (net5.0, net6.0, net7.0, net9.0) that were not in the TargetFrameworks list. This created a mismatch between the conditional checks and the actual build targets.

Updated the conditional to only check for net8.0 and net10.0 — the frameworks actually defined in TargetFrameworks that support implicit usings.

<!-- Before -->
<PropertyGroup Condition="
  '$(TargetFramework)' == 'net5.0' OR
  '$(TargetFramework)' == 'net6.0' OR
  '$(TargetFramework)' == 'net7.0' OR
  '$(TargetFramework)' == 'net8.0' OR
  '$(TargetFramework)' == 'net9.0' OR
  '$(TargetFramework)' == 'net10.0'
  ">

<!-- After -->
<PropertyGroup Condition="
  '$(TargetFramework)' == 'net8.0' OR
  '$(TargetFramework)' == 'net10.0'
  ">

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Refactor

How Has This Been Tested?

• Built solution for all target frameworks (net462, netstandard2.0, net8.0, net10.0)
• Code review passed
• Security scan passed

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Screenshots (if applicable)

N/A

Additional context

Addresses review feedback from PR #20 regarding conditional compilation alignment.

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