Create copilot-instructions.md for improving code reviews, Fixes AB#3384872

[shahzaibj]

Fixes AB#3415429

[github-actions]

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[Copilot]

Pull Request Overview

This PR introduces comprehensive code review guidelines for the Common Android Auth Library by creating a new copilot-instructions.md file. The document aims to standardize AI-assisted and human code reviews with detailed domain-specific guidance for authentication library development.

Key Changes:

• Establishes baseline code review principles including language-specific keyword handling and context-appropriate feedback
• Provides extensive domain knowledge covering architecture layers, token lifecycle, cache model, cryptography, telemetry, and IPC schema compatibility
• Defines security, concurrency, testing, and performance review criteria with concrete examples and anti-patterns

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_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}