(feat: add AgentRegistryToolProvider for centralized agent discovery and messaging)

• Add AgentRegistryToolProvider class with registry-based agent discovery
• Implement tools for finding agents by skill, best agent selection, and similarity matching
• Support direct messaging to registry agents with A2A protocol integration
• Add comprehensive test suite with full coverage of all registry operations
• Include JSON-RPC client for registry communication and agent card management

Description

Adds AgentRegistryToolProvider for centralized agent discovery and messaging capabilities.

Changes

• Add AgentRegistryToolProvider class with registry-based agent discovery
• Implement tools for finding agents by skill, best agent selection, and similarity matching
• Support direct messaging to registry agents with A2A protocol integration
• Add comprehensive test suite with full coverage

Related Issue

Closes #265

Documentation PR

n/a

Type of Change

New Tool

Testing

How have you tested the change? Verify that the changes do not break functionality or introduce warnings in consuming repositories: agents-docs, agents-tools, agents-cli

• I ran hatch run prepare

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature
• My changes generate no new warnings
• Any dependent changes have been merged and published

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