Add configurable newline option for dump output

[smurtdev]

Summary

• Add DumpOptions.NewLine so string dump output can explicitly use LF or CRLF regardless of OS
• Apply the configured newline to both C# and Visual Basic dumpers while preserving existing TextWriter.NewLine behavior unless DumpOptions.NewLine is explicitly set
• Add focused tests for configurable newlines, cloning, validation, and TextWriter restoration
• Make dump output assertions line-ending agnostic so the suite runs green on Linux and Windows

Verification

• dotnet build VarDump.sln --configuration Release --no-restore
• dotnet test test/VarDump.UnitTests/VarDump.UnitTests.csproj --configuration Release --no-build --framework net6.0
• dotnet test test/VarDump.UnitTests/VarDump.UnitTests.csproj --configuration Release --no-build --framework net9.0
• dotnet test test/VarDump.Extensions.UnitTests/VarDump.Extensions.UnitTests.csproj --configuration Release --no-build --framework net6.0
• dotnet test test/VarDump.Extensions.UnitTests/VarDump.Extensions.UnitTests.csproj --configuration Release --no-build --framework net9.0