abort_on_code_timeout; better error handling

[snimu]

Description

Small fixes to make the RLMEnv run with current verifiers.

• fixes sandbox startup & python installation process
• adds abort_on_code_timeout parameter
  • set to False to give the model an error message on sandbox execution timeout
  • set to True to stop the rollout with an error on sandbox execution timeout; this is useful because some models just keep writing inefficient code until their context window is full, which can take a very long time

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Test improvement

Testing

• All existing tests pass when running uv run pytest locally.
• New tests have been added to cover the changes

Checklist

• My code follows the style guidelines of this project as outlined in AGENTS.md
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Additional Notes

---

Note

Introduce abort_on_code_timeout to control rollout on code timeouts; improve worker startup synchronization, adjust timeouts, and return structured errors on execution timeouts.

• RLMEnv:
  • Timeout behavior:
    • Add abort_on_code_timeout flag; on code CommandTimeoutError, either abort rollout or return a structured error to the model.
    • Set documented code_execution_timeout default to 120 and remove retry in code execution.
  • Sandbox worker startup:
    • Wait for worker script after pip installs; simplify spawn logic and tune sleeps/iterations.
    • Use explicit timeouts for start and ready checks, with clearer failure messages and debug info.
  • Error handling:
    • Standardize exception chaining (raise vf.SandboxError() from e) across startup and execution paths.

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