fix: documentation issues (#92, #132, #173)

[terrier989]

No description provided.

[Copilot]

Pull Request Overview

This PR fixes documentation errors in code examples across three files, correcting variable names and API usage to match the actual implementation.

• Corrected incorrect variable reference in cipher.dart example (using sink instead of undefined encryptedSink)
• Updated RsaPss instantiation to use the factory constructor pattern (RsaPss.sha256())
• Fixed method call to extract bytes from the correct object (sharedSecret instead of aliceKeyPair)

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
cryptography/lib/src/cryptography/cipher.dart	Fixed variable name in documentation example from encryptedSink to sink to match the declared variable
cryptography/lib/src/cryptography/algorithms.dart	Updated RsaPss instantiation pattern from constructor to factory method (RsaPss.sha256())
cryptography/README.md	Corrected method call to extract bytes from sharedSecret instead of aliceKeyPair in key agreement example

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