feat: add runtimeClient passthrough support

[nborges-aws]

Issue #: #391

Summary:
Previously, there was no way for customers to programmatically manage agent runtime resources (create, update, delete runtimes/endpoints) through the SDK. This PR adds passthrough plumbing, so allowlisted bedrock-agentcore-control and bedrock-agentcore methods are callable directly on AgentCoreRuntimeClient with snake_case kwarg support. This follows the same pattern established in MemoryClient.

Description of changes:

• Add getattr passthrough with accept_snake_case_kwargs to AgentCoreRuntimeClient, enabling direct access to allowlisted boto3 control plane and data plane methods
• Create underlying cp_client (bedrock-agentcore-control) and dp_client (bedrock-agentcore) boto3 clients in init
• Added utility methods for create and wait, teardown, and aggregated status
• Control plane allowlisted methods:
  • create_agent_runtime
  • update_agent_runtime
  • get_agent_runtime
  • get_agent_runtime_endpoint
  • delete_agent_runtime
  • delete_agent_runtime_endpoint
• Data plane allowlisted methods:
  • invoke_agent_runtime
  • stop_runtime_session

Test plan

• - test_init_default_region — session region used when no explicit region
• - test_init_default_region_fallback — falls back to us-west-2
• - test_init_creates_boto3_clients — verifies both CP and DP clients created
• - test_init_with_integration_source — verifies param stored
• - test_cp_method_forwarded — CP method forwards to cp_client
• - test_dp_method_forwarded — DP method forwards to dp_client
• - test_snake_case_kwargs_converted — agent_runtime_id → agentRuntimeId
• - test_non_allowlisted_method_raises_attribute_error — unknown method → AttributeError
• - test_all_cp_methods_in_allowlist / test_all_dp_methods_in_allowlist — assert exact allowlist contents
• - All existing tests pass (44/44)

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[github-actions]

⚠️ Breaking Change Warning

Found 1 potential breaking change(s) in this PR:

�[1msrc/bedrock_agentcore/runtime/agent_core_runtime_client.py�[0m:71: AgentCoreRuntimeClient.region: �[33mAttribute value was changed�[39m: region -> region or session.region_name or 'us-west-2'

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Note: This is an automated static analysis check. Some flagged changes may be intentional.
Please confirm each item is expected and, if so, add a migration note to CHANGELOG.md.

[Hweinstock]

I feel like we shouldn't default region, but I know this is against the existing pattern. @jariy17 what do you think?

[Hweinstock]

q: how long does a runtime take to be ready? I know memory takes like 3 minutes so we have a create_and_wait utility. Wondering if the same could be useful here. Could come as a follow-up.

[nborges-aws]

Yep I had the same thought. Added utilities for wait on create

[tejaskash]

Looks good. Follows the established MemoryClient passthrough pattern cleanly. Good test coverage across polling, timeouts, failure states, and teardown ordering.