chore: update dependencies and build tooling

[niemyjski]

Summary

• update the .NET SDK and all compatible stable NuGet dependencies across core libraries, target-specific integrations, tests, and samples
• keep net8.0 and net9.0 Microsoft.Extensions references on their matching major lines while updating each to its latest supported release
• update official GitHub Actions to checkout v7.0.1 and setup-dotnet v6.0.0, pinned to immutable commit SHAs
• update and pin workflow tools, move the devcontainer to the current official .NET 10 image, and add Dependabot coverage for GitHub Actions and devcontainers

Security and provenance

• dotnet list Exceptionless.Net.Windows.slnx package --vulnerable --include-transitive: no vulnerable packages
• dotnet list Exceptionless.Net.Windows.slnx package --deprecated --include-transitive: no deprecated packages
• osv-scanner scan source --recursive .: no issues across all 28 manifests, including the legacy MVC packages.config
• downloaded and verified all 20 updated NuGet archives; every content hash and available NuGet signature verified successfully
• resolved the action releases through the official repositories and pinned their exact release commits
• verified the Microsoft devcontainer tag and digest in MCR

Validation

• dotnet build --configuration Release Exceptionless.Net.NonWindows.slnx: succeeded, 0 warnings
• dotnet test --configuration Release --no-build Exceptionless.Net.NonWindows.slnx: 310 passed, 18 existing skips
• Windows-shaped Release build across net462, net472, net8.0, net9.0, and net10.0: succeeded, 0 warnings
• Windows-shaped and non-Windows package creation: succeeded
• all 7 SDK-style cross-platform samples: Release build succeeded, 0 warnings
• Windows Forms and WPF samples: cross-targeted Release build succeeded for modern Windows and net462, 0 warnings
• console sample: launched and exercised the upgraded client/NLog path
• exact MinVer 7.0.0 and gpr 0.1.294 workflow tools: installed and executed successfully on the current SDK
• final compatible-version audit: no outdated dependencies
• all GitHub YAML files parse successfully

Sample runtime boundary

The legacy MVC, WCF, and Web Forms samples were attempted but require Visual Studio WebApplication targets and .NET Framework developer packs that are unavailable on macOS. ASP.NET Core and Blazor dev-host startup stalls were reproduced unchanged on untouched origin/main, so they are pre-existing runtime/toolchain behavior rather than regressions from this branch.

Coordination

This consolidates and supersedes the package updates in #361, #362, #363, #364, and #365. Open feature PRs #367 and #368 were inspected but intentionally not absorbed because their MAUI and serializer/DI changes are not on main; #368 will have a small src/Exceptionless/Exceptionless.csproj rebase overlap.