Add durable AgentCore agent example

[lennessyy]

Summary

• add a long-running Strands agent modeled as a Temporal Workflow
• run model and AgentCore Code Interpreter calls as Temporal Activities
• include local and AgentCore Runtime Workers with an activity-based idle policy
• test that conversation messages survive replacement of the Worker process
• add Snipsync markers for the companion documentation guide

Verification

• uv run ruff check .
• uv run ruff format --check .
• uv run mypy --check-untyped-defs .
• uv run pytest -q
• agentcore validate

Status

Draft while AgentCore Serverless Workers support and the companion documentation are in pre-release.