Proposal: Add ACAExecutor for Azure Container Apps Sandboxes

[SharmaAjay19]

Proposal: Add ACAExecutor for Azure Container Apps Sandboxes

We would like to contribute a first-class ACAExecutor to smolagents so developers can
run CodeAgent-generated Python in
Azure Container Apps Sandboxes using the
same executor_type experience as the existing E2B, Modal, Docker, and Blaxel
integrations.

The proposed user experience is:

from smolagents import CodeAgent, InferenceClientModel

with CodeAgent(
    tools=[],
    model=InferenceClientModel(),
    executor_type="aca",
    executor_kwargs={
        "region": "<azure-region>",
        "subscription_id": "<subscription-id>",
        "resource_group": "<resource-group>",
        "sandbox_group": "<sandbox-group>",
    },
) as agent:
    result = agent.run("Analyze the data and return the result.")

Initial functionality

ACAExecutor would provide:

• Persistent remote Python execution, preserving variables and imports across agent
  steps.
• Existing smolagents remote-executor behavior for tools, transferred variables,
  additional package installation, logs, rich outputs, errors, and final_answer.
• Isolated, provider-managed execution for model-generated code.
• Azure authentication through the standard Azure credential chain, without placing
  Azure credentials inside the sandbox.
• Automatic creation and deterministic cleanup of executor-owned sandboxes.
• An optional smolagents[aca] dependency extra so Azure packages remain opt-in.
• Support for Python 3.10 and current Python releases, with mocked unit tests and a gated
  live integration test.

The initial contribution would focus on CodeAgent remote execution. Cross-process
session resume and managed-agent execution would remain out of scope until their
lifecycle contracts are defined.

The Microsoft ACA Sandboxes team would contribute the implementation, tests, examples,
and documentation, and help maintain compatibility with the underlying Azure SDK.

Before starting, we would appreciate maintainer feedback on:

1. Whether a native ACAExecutor and executor_type="aca" are a good fit for
   smolagents.
2. Whether the implementation should live with the existing remote executors or in a
   provider-specific module.
3. Any preferred conventions for optional dependencies, live tests, and ongoing
   provider maintenance.

[SharmaAjay19]

@albertvillanova What do you think? Let me know and I can raise a PR.