Refactor project dependencies

[martincostello]

• Split dependencies into groups to make management easier.
• Remove MSBuild variables for versions.
• Fix samples using .NET 8 instead of 9.
• Remove redundant properties.
• Sort some properties.
• Update test behaviour for Microsoft.Extensions.TimeProvider.Testing upgrade due to changes in Respect AutoAdvance for GetTimestamp in FakeTimeProvider dotnet/extensions#5783.

Resolves dependabot alerts for CVE-2024-30105 and CVE-2024-43485 in the DependencyInjection sample.

[Copilot]

Pull Request Overview

This PR refactors project dependencies to improve maintainability and security, splitting dependencies into logical groups while removing MSBuild variables for version management. The changes standardize all sample projects to use .NET 9.0 and move common properties to Directory.Build.props files.

• Consolidates common project properties into Directory.Build.props files
• Updates sample projects from .NET 8.0 to .NET 9.0 for consistency
• Removes MSBuild variables and replaces them with explicit version declarations

Reviewed Changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/Polly.Core.Tests/Retry/RetryResilienceStrategyTests.cs	Updates test to use standard FakeTimeProvider instead of custom throwing implementation
samples/*/*.csproj	Removes redundant project properties that are now inherited from Directory.Build.props
samples/Directory.Build.props	Adds common properties like ImplicitUsings and Nullable, sorts properties alphabetically
Directory.Packages.props	Removes MSBuild variables and replaces with explicit version declarations grouped by purpose
Directory.Build.props	Adds ManagePackageVersionsCentrally property
.github/dependabot.yml	Adds Polly package grouping for dependabot updates

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.23%. Comparing base (a4b66fb) to head (96f1f6f).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2696   +/-   ##
=======================================
  Coverage   96.23%   96.23%           
=======================================
  Files         311      311           
  Lines        7322     7322           
  Branches     1012     1012           
=======================================
  Hits         7046     7046           
  Misses        222      222           
  Partials       54       54           

Flag	Coverage Δ
linux	96.23% <ø> (ø)
macos	96.23% <ø> (ø)
windows	96.22% <ø> (ø)

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[martincostello]

Manually verified the versions referenced by the various TGMs in the NuGet packages haven't been changed.