docs: prepare 0.13.3 high-dimensional docs release

[0xC000005]

Summary

• add examples/SliderPartitionValidation, a runnable 8D Slider example that compares a correct grouped partition against an intentionally weak singleton partition
• expand Slider docs with a mental model, partition-selection workflow, and held-out validation snippet
• improve Tensor Train docs with a core-chain mental model, complete quick start, TT-Cross validation checklist, and troubleshooting table
• advance package metadata to 0.13.3, update package validation baseline to 0.13.2, and add the 0.13.3 changelog entry
• run VSTest with parallelization disabled to avoid the existing Console.Out capture race in verbose-output tests

Fixes #185.

Supersedes #186 and #187 by combining the high-dimensional docs work into one versioned patch-release PR.

Validation

• dotnet restore -p:NuGetAudit=false
• dotnet format --verify-no-changes --verbosity minimal --no-restore
• git diff --check
• dotnet build --configuration Release --verbosity minimal --tl:off -p:NuGetAudit=false
• dotnet run --configuration Release --no-build --project examples/QuickStart/QuickStart.csproj
• dotnet run --configuration Release --no-build --project examples/SliderPartitionValidation/SliderPartitionValidation.csproj
• dotnet run --configuration Release --no-build --project examples/TensorTrainHighDim/TensorTrainHighDim.csproj
• dotnet test tests/ChebyshevSharp.Tests/ChebyshevSharp.Tests.csproj --configuration Release --no-build --verbosity minimal --collect:"XPlat Code Coverage" -- RunConfiguration.DisableParallelization=true
• dotnet pack src/ChebyshevSharp --configuration Release --no-build --output artifacts/packages
• docfx docs/docfx.json

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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