Add cargo-nuspec crate - CLI tool to generate .nuspec files

[Copilot]

This PR implements a new cargo-nuspec crate that provides a cargo subcommand for generating .nuspec files from Rust package metadata.

Features

The cargo-nuspec tool can be installed as a cargo subcommand and used to generate NuGet package specification files:

cargo install cargo-nuspec
cargo nuspec <package-name>

The tool automatically maps Cargo.toml metadata to NuGet package specifications:

• Package name → NuGet package id
• Version → NuGet package version
• Description → NuGet package description
• Authors → NuGet package authors
• Homepage → NuGet project URL
• License → NuGet license expression
• Repository → NuGet repository URL
• Keywords → NuGet tags

Usage Examples

Generate a .nuspec file for a package in your workspace:

cargo nuspec my-package

Specify a custom output directory:

cargo nuspec my-package -o /path/to/output

Use with a different workspace:

cargo nuspec my-package -m /path/to/workspace/Cargo.toml

Implementation Details

• Built using clap for CLI argument parsing and cargo_metadata for reading package information
• Integrates with the existing nuspec crate for XML generation
• Includes comprehensive error handling and unit tests
• Follows cargo subcommand conventions for seamless integration

The generated .nuspec files can be used directly with nuget pack to create NuGet packages from Rust projects.

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