Migrate OpenCvSharp.sln to the .slnx solution format

[shimat]

Summary

• Replaced OpenCvSharp.sln with OpenCvSharp.slnx (generated via dotnet sln OpenCvSharp.sln migrate), and updated the one active doc reference (docs/build-instructions.md) to point at the new file.
• No CI workflow builds OpenCvSharp.sln directly (all Windows/Linux/macOS pipelines build individual .csproj/CMake targets), so this has no build-pipeline impact.
• This repo already targets net10.0/.NET 10 SDK and builds with the VS 2026 generator in CI, and .slnx is fully supported by VS 2022 17.13+, VS 2026, Rider 2024.3+, and the .NET 10 SDK CLI, so this isn't a premature move.

Test plan

• Verified a full Release|x64 build through VS 2026's MSBuild.exe against OpenCvSharp.slnx succeeds end-to-end (native OpenCvSharpExtern.vcxproj + all managed projects + OpenCvSharp.Tests/.Tests.Windows/.Tests.Avalonia), exit code 0.
• CI passes unaffected (doesn't touch the solution file at all)

Summary by CodeRabbit

• Build & Development
  • Migrated the Visual Studio solution to the newer .slnx format.
  • Updated the solution’s build configurations and platforms to match the prior setup.
  • Updated Windows build instructions to reference the new solution file.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: e62485f2-c80d-4c6b-9d9d-79d4b86feb8d

📥 Commits

Reviewing files that changed from the base of the PR and between 5c0ff95 and ecd489e.

📒 Files selected for processing (1)

• docs/build-instructions.md

🚧 Files skipped from review as they are similar to previous changes (1)

• docs/build-instructions.md

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📝 Walkthrough

Walkthrough

The legacy OpenCvSharp.sln file was removed and replaced with OpenCvSharp.slnx, which lists solution projects and build configurations. Windows build instructions now reference the new solution filename.

Changes

Solution migration

Layer / File(s)	Summary
Solution definition and build entry point OpenCvSharp.slnx, docs/build-instructions.md	The new solution defines project entries, platforms, configurations, solution items, and native project build rules; Windows Step 4 now opens OpenCvSharp.slnx.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: replacing the .sln solution with a .slnx format.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch migrate-sln-to-slnx

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@docs/build-instructions.md`:
- Line 52: Update the build instructions around OpenCvSharp.slnx to state that
opening or building it requires Visual Studio 2022 version 17.12 or later, or
another supported toolchain. Preserve the existing build guidance while clearly
qualifying the .slnx requirement.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 99e22dd3-9094-4865-a68d-b58816eab8aa

📥 Commits

Reviewing files that changed from the base of the PR and between b16529f and 5c0ff95.

📒 Files selected for processing (3)

• OpenCvSharp.sln
• OpenCvSharp.slnx
• docs/build-instructions.md

💤 Files with no reviewable changes (1)

• OpenCvSharp.sln