feat: onchain feature flag registry

[coffeexcoin]

• create onchain feature flag registry
• add events; use address 0 for global status
• clean up
• remove redundant check

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PR-Codex overview

This PR introduces a new FeatureFlagRegistry smart contract for managing feature flags on-chain, adds support for an abstractMainnet network configuration, and refines deployment scripts to utilize a create2IfNotExists utility function.

Detailed summary

• Added abstractMainnet network configuration to hardhat.config.ts.
• Introduced FeatureFlagRegistry contract in contracts/helpers/FeatureFlagRegistry.sol.
• Updated deployment scripts to use create2IfNotExists function.
• Removed redundant create2IfNotExists function from deployment scripts.
• Enhanced create2IfNotExists function to include network configuration and deployment checks.

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