Fix Pinget UniGetUI JSON contract and Rust/C# parity

[Marc-André Moreau (mamoreau-devolutions)]

Summary

• normalize the UniGetUI-facing Pinget JSON contract
• add explicit JSON contract tests for the C# and Rust CLIs
• fix Rust plain \list\ correlation so canonical WinGet package IDs and \SourceName\ are returned instead of raw ARP IDs
• keep \LocalId\ as the raw installed identity while returning canonical package \Id\

Validation

• dotnet test dotnet/src/Devolutions.Pinget.Core.Tests/Devolutions.Pinget.Core.Tests.csproj -c Release
• cargo test -p pinget-core --manifest-path rust/Cargo.toml
• cargo test -p pinget-cli --manifest-path rust/Cargo.toml
• cargo build -p pinget-cli --manifest-path rust/Cargo.toml
• manual UniGetUI Avalonia verification with both C# and Rust bundled Pinget builds