docs: Add Filecoin Solidity Library FAQ

[snissn]

PR: Add Filecoin Solidity Library FAQ

Overview

This PR introduces a comprehensive FAQ (FAQ.md) to the repository, addressing common questions and clarifications about the Filecoin Solidity Library. The goal is to provide developers with clear guidance on integrating the library, reducing confusion, and improving usability.

Key Topics Covered

✅ Serialization and Address Handling – Differences between serializeAddress implementations and best practices for buffer allocation.
✅ BigInt Handling – Explanation of zero representations, serialization optimizations, and consistent handling.
✅ Allowance and Token Transfers – How transferFrom, withdrawBalance, and addBalance behave in different scenarios.
✅ Filecoin Actor Calls – Expected return behaviors for missing data, handling of publishStorageDeals, and large data responses.
✅ Miner API – Clarification on slashed/terminated miners and ownership rules for CreateMiner.
✅ Power API – Explanation of minerCount and its inclusion/exclusion of terminated miners.
✅ Security and Error Handling – Best practices for using require vs. assert, and guidance on Filecoin precompiles.

Why This Is Needed

• Provides clear, structured documentation based on developer discussions and audit insights.
• Helps reduce onboarding friction for developers integrating Filecoin Solidity contracts.
• Ensures best practices are well-documented for contract interactions and actor calls.

Implementation Details

• The FAQ is included as FAQ.md in the root of the repository.
• Content is designed to be self-contained, ensuring that developers do not need to reference external discussions to understand key concepts.
• Formatting follows developer-friendly markdown standards, making it easy to read and navigate.