Update Microsoft.Bcl.Cryptography nuget package text

[vcsjones]

SEO-ify the package text with PQ types and add a using so our example shows a good practice.

I don't know if we really need a "how to use" code snippet, so I would be open to removing it entirely. M.B.C has become kind of "Crypto stuff we need down level" and less of anything we are trying to coherently package.

[Copilot]

Pull Request Overview

This PR updates the Microsoft.Bcl.Cryptography NuGet package documentation to improve SEO and demonstrate best practices. The changes add post-quantum cryptography (PQ) algorithm types to the package description and modify the code example to show proper disposal pattern usage.

• Adds four new post-quantum cryptographic algorithm types to the main types list
• Updates the code example to use the using statement for proper resource disposal

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[vcsjones]

/ba-g markdown only change