feat: Add BlockRun action provider for pay-per-request LLM access

[1bcMax]

Summary

Add BlockRun action provider enabling AI agents to access multiple LLM providers (OpenAI, Anthropic, Google, DeepSeek) using pay-per-request USDC micropayments on Base chain via the x402 protocol.

Why BlockRun?

• Multi-provider access: GPT-4o, Claude, Gemini, DeepSeek via single integration
• Pay-per-request: No monthly subscriptions - pay only for what you use in USDC
• Secure: Private key never leaves your machine (local EIP-712 signing)
• Native x402: Built on Coinbase's x402 protocol - a natural fit for AgentKit

Changes

• Added BlockrunActionProvider with chat_completion and list_models actions
• Added blockrun-llm as optional dependency (pip install coinbase-agentkit[blockrun])
• Updated action providers exports
• Added documentation and changelog entry

Actions Provided

Action	Description
chat_completion	Send chat completion requests to LLMs via x402 micropayments
list_models	List available models (GPT-4o, Claude, Gemini, DeepSeek)

Usage Example

from coinbase_agentkit import (
    AgentKit,
    AgentKitConfig,
    blockrun_action_provider,
)

agentkit = AgentKit(AgentKitConfig(
    wallet_provider=wallet_provider,
    action_providers=[blockrun_action_provider()],
))

Testing

• Syntax validation passes
• Ruff linting passes
• Code follows existing action provider patterns (similar to hyperbolic_action_provider)

Links

• BlockRun Documentation
• x402 Protocol
• Python SDK

[cb-heimdall]

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