refactor(domain): standardize metadata field naming to meta_data across all models
- Rename metadata fields to meta_data for consistency across domain models
- Update agent_identity, agent_performance, agent_portfolio, amm, analytics, bounty, certification, community, cross_chain_bridge, cross_chain_reputation, decentralized_memory, miner, pricing_models, trading, and wallet models
- Rename chain_metadata to chain_meta_data in CrossChainMapping
- Rename verification_metadata to verification_meta_data
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