feat(agentgateway): add global id filter for lob agents

[I542102]

Summary

• Adds a global ID filter capability for LOB agents in the Agent Gateway client
• Introduces new filter fragments in _fragments.py to support filtering by global ID
• Extends _models.py with the corresponding filter models
• Updates _lob.py and agw_client.py to wire the new filter through the query path

Test plan

• Unit tests added in tests/agentgateway/unit/test_agw_client.py covering the new filter logic
• Unit tests added in tests/agentgateway/unit/test_lob.py for LOB-specific filter behavior
• Run pytest tests/agentgateway/ locally to verify all tests pass

[cla-assistant]

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